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THE AMERICAN NATURALIST

THE We

AMERICAN NATURALIST

A MONTHLY JOURNAL

DEVOTED TO THE ADVANCEMENT OF THE BIOLOGICAL SCIENCES

WITH SPECIAL REFERENCE TO THE FACTORS OF EVOLUTION

VOLUME XLV

Mo. Bot, Garden

1912

NEW YORK

THE SCIENCE PRESS

IQII

THE

AMERICAN NATURALIST

VoL. XLV : January, 1911 No. 529

ORGANIC RESPONSE!

D. T. MACDOUGAL, Px.D., LL.D.

Desert LABORATORY, Tucson, ARIZ.

Ar no time in the history of natural science has such

a large share of thought and research energy been di-

rected to the solution of evolutionary problemsas at pres-

ent. Methods of work, plans for experimentation and

modes of interpretation have recently undergone such

rapid development and improvement that our potenti-

ality for solving questions in heredity and origination is

vastly greater than even at such recent date as the be-

ginning of this new century. With increased facility

in attack has also come wider vision and altered view-

points with regard to almost all phases of biology.

Biological thought once quickened and broadened by

evolutionary ideas was by this same means led to be-

come entangled in a maze of illusive assumptions as to

purpose and plan in organisms from which it is being but

slowly freed, to view functions as inevitable reactions,

however complex they may be. The variables included

in the equations of protoplasmic action are numerous

and large, but they do not exceed the undefined prin-

ciples of osmotic action, surface tension and unknown

phases of association and dissociation that are concerned

in the interplay of substances in the cell, and upon which

1 Presidential sigan Society of American Naturalists, Ithaca, New

York, December 29,

5

6 THE AMERICAN NATURALIST [ Vot. XLV

depend the chemico-physical relations of tissue compo-

nents and structures of all kinds. If physiology escapes

the soporific and deadening influence of the vitalistic con-

ceptions, now appearing in some profusion, it may in turn

furnish the secure means for a long and rapid advance

in genetics, and it may be assumed with some certainty

that the chief superstructures of evolutionary science will

be those securely raised upon a foundation of physiolog-

ically tested facts.

In taking this direction, natural history is not alone;

the briefest comprehensive view of the physical sciences

will show that here also the chief advance lies along the

way of the study of energetics, and that the fundamental

problems are those lying about the mode and means of

transformations of energy.

Recent events in the field of evolution comprehend a

number of movements and accomplishments of extraor-

dinary interest. The rediscovery of the facts of alter-

native inheritance, the formulation of the concepts of

equivalent, balanced, paired or differential characters, the

results of statistical studies of variability, the analyses

of species of various constitution by pedigree cultures, in

which the value of fertilization from various sources is

carefully measured, the distinction of the biotype or geno-

type as a hereditary entity, the possibilities in the ac-

tion of pure lines within a specific group, the cytological

contributions of fact and forecast upon the physical as-

pects of heredity, and lastly the presentation of the facts

and allowable generalizations identified with the muta-

tion theory, comprise a series of advances, of accretions

to knowledge, furnish a broadened foundation for biolog-

ical science, and disclose additional possibilities in all lines

of experimental research with living things, besides open-

ing up new realms for speculative thought, and stimulat-

ing the scientific imagination to renewed fruitfulness.

Biological literature has also been recently enriched by

a series of formal papers commemorative of the life and

work of Charles Darwin, by more than fourseore workers

No. 529] ORGANIC RESPONSE A

representing the laboratories and national cultures of

the world. This group of addresses and essays, fortu-

nately written chiefly within four languages, taken col-

lectively, constitutes a critical and evaluatory discussion

of the mass of fact and galaxy of theory concerning or-

ganic evolution, and furnishes the most complete and

thorough appraisal ever made of any subject in modern

biology.

The moment, therefore, is one of consciousness of

achievement, of realization of increased powers of pene-

tration, and charged with desire for the exploitation of

the unknown, and is vibrant with the inspiration coming

from such a rapid march of events. With this quick-

ening in activity, the outeries of acrid controversies no

longer monopolize our attention, but it must not be sup-

posed that differences of opinion have vanished from

among us. The agreement as to the value of methods

of experimentation and calibration is a most gratifying

fact, but the harmonies of opinion as to interpretation of

results have not yet come to a monotone.

On the contrary, the pressure of new and undisciplined

evidence has awakened a freshened chorus of voices cry-

ing the virtues of special interests and extolling the suff-

ciency of theories dignified by age and more or less

weighty with authority. Those busy with vitalism of

various patterns have spun a moiety of their favorite

fabric to mend the breaks in the fragile web made by the

impact of new facts. Isolation and the mechanism of

geographical distribution have again been elaborated to

account for all differentiation and what their exponents

are pleased to term speciation. The anticipatory forma-

tion of structures in a rudimentary condition with a long

prefunctional progress, guided by the morphological pos-

sibilities and actuated by internal impulses, has again

been offered to us, fortified by paleontological fact and

clever logic, in such manner as to avoid most of the serious

objections to orthogenesis except those of physiological

morphology.

8 THE AMERICAN NATURALIST [Vou. XLV

Natural selection with diverse meanings and manifold

implications has been made to explain development, dif-

ferentiation and general evolutionary progress. The tu-

mult'is greatest at the present time, however, about the

idea of mutation. Standing to one side, the biologist

hears a medley of assertions ‘‘that mutations have long

been known,” ‘‘do not exist,’’ ‘‘were discovered by Dar-

win,’’ ‘‘are always an evidence of hybridization,’’ ‘‘re-

sult in the formation of nothing but elementary species,”’

‘sive only weakened derivatives that are quickly

swamped by parental forms,’’ ‘‘are encountered only

among cultivated plants,’’ ‘‘the mutation theory is based

upon the conception of unit characters,’’ ‘‘constitutes the

only adequate means of accounting for the enormous

number of living forms and myriad characters of living

things,’’ ‘‘unit characters are unreal, have never been

seen, do not exist and are incapable of demonstration.’’

‘‘The difference between mutation and variation is one of

amplitude only,’’ and lastly mutation signally ‘‘refutes

Darwinism,’’ and ‘‘swings us back in harmony with the

theologian’s arguments for special creation.’’

The absurdity of the many injudicial assertions by the

partisans concerned need not blind us to the stubborn

fact that saltatory changes do occur in hereditary pure

lines in a large number of forms in both plants and

animals. Observations and experiments have estab-

lished beyond doubt that mutation is one way by which

organisms bearing new combinations of qualities may

arise, although it is probable that its importance as a

general procedure varies in different groups of organisms

and certain that many shades of opinion as to its exact

part in the evolution of living things will always be held.

Our appraisement of the value of all the protheses

cited may also be amended from time to time with view-

points altered by the advance of knowledge. The situa-

tion with regard to one hypothesis is far more serious,

however. This is the theory which predicates direct

adaptational adjustment of the organism, quickly or

No. 529] ORGANIC RESPONSE 9

slowly as the case may be, to environie factors, and

the inheritance of the somatic alterations constituting

such variations. The various corollaries of this theory

have the force of a certain obviousness, its assumptions

have been of ready service to the systematist and bio-

geographer, and its conclusions have long been tolerated

in the absence of decisive tests which are not to be easily

made or readily carried out. The time has now arrived,

however, when the claimants for Neo-Lamarckianism and

all of its conclusions must show cause for its further con-

sideration, or else allow it to drop from the position of

being seriously taken as a method of evolutionary advance.

It is unanimously agreed that organisms, plants as well

as animals, change individually in aspect, in form and

structure of organs, in functionation and habit as they

encounter swamps, saline areas, gravelly uplands or

slopes, climatic differences identifiable with latitude or

elevation, and other physical and biological factors. It is

assumed that these somatic alterations are accommodative

and adaptive, making the organism more suitable for the

conditions which produce the changes. Such an assump-

tion is an over-reaching one. Any analysis of the changes

which an organism undergoes after transportation to a

new habitat will disclose one or a few alterations which

might be of advantage in dealing with the newly encoun-

tered conditions, but with these are many others, direct,

necessitous, atrophic, or hypertrophic as to organs which

have no relation whatever to usefulness or fitness. Fur-

ther, a critical examination fails to disclose any theoret-

ical considerations or any actual facts which would con-

nect inevitably the somatic response with the nature of

the excitation, outside of the specialized tropisms in

which specific reactions are displayed. Even in these

the adjustment is of such nature that a mechanism spe-

cially perceptive to contact, for example, may react to

changes in temperature, as illustrated by the action of

tendrils, and many similar cases might be cited. It is

evident that the soma of a plant or animal is not to be

10 THE AMERICAN NATURALIST [ Vou. XLV

considered as capable of adaptive alterations to every new

agency which may cause changes in its form, structure

or functionation.

Next we come to the very crux of the whole matter: do

the unusual forms or activities of organs resulting from

environic causes act in any manner upon the germ-plasm

connected with such altered bodies? If we are to con-

sider the activities of the organism or of the cell to de-

pend mainly upon its chemical structure and constituency

and such a generalization seems unavoidable, then we

have means by which the soma might cause its proper-

ties to be reflected from the germ-plasm in a succeeding

generation, since the chemical mechanism of the soma

and germ-plasm must be of the most intimate nature.

That some such connection does actually exist is strongly

suggested by the behavior of a great number of organ-

isms which have been seen to carry marked environic

effects to the second or even third generations; if the

interrogation be made as to why the induced qualities are

earried no further it may be said that the reply may be

suggested by the results of long-continued action of the

exciting agency, such as has been used by Woltereck with.

Daphnia.

If a general view be taken of the available information

of interest in this connection, three classes of facts will

be discerned. One group is comprised in the mass of in-

formation obtained by the operations of the horticul-

turist, the agriculturist and the breeder as to the behav-

ior of crops, plants and domestic animals, when trans-

ferred from one habitat to another. The greater part of

such data is the result of observations which do not com-

ply with the ordinary requirements in the avoidance of

error so that strict comparisons as to the behavior of

organisms under conditions of various habitats are im-

possible. A consideration of the literature yields many

suggestions for experimental research and the simple

generalization that the direct effects of climatic com-

plexes on the seasonal cycle, and upon color, or struc-

No. 529] ORGANIC RESPONSE 11

tural features of the individual, may be repeated or car-

ried over two or three generations, in a habitat where

the specific causal combinations are lacking. This is the

available total of knowledge furnished us by economic

operations, and by the introduction operations of botan-

ical gardens and plantations.

In contrast with these the fortunate experience of Zed-

erbauer with Capsella has yielded some conclusions of

exceptional importance. A genotype of Capsella Bursa-

pastoris resembling taraxicafolium was found on the |

lower plains of Asia Minor, and displayed the well-

known characters of this form, including broad leaves,

whitish flowers, and stems 30-40 em. high. A highway

leads from these regions to a plateau at an elevation of

2,000 to 2,400 meters. The conditions of distribution are

such as to indicate that the plant has been carried up

this thoroughfare by man, and in this elevated habitat

it has taken on certain alpine characters, including elon-

gated roots, xerophytic leaves, stems 2-5 em. high, red-

dish flowers, with a noticeable increase of the hairiness

of the entire plant. That the distributional history has

been correctly apprehended seems entirely confirmed by

the fact that when seeds are taken from the lowlands the

alpine characters enumerated are displayed at once as a

direct somatic response. When seeds are taken from

plants on the elevated plateau where their ancestors may

have been for many years or many centuries (perhaps as ,

long as 2,000 years) and sowed at Vienna and in other cul-

tures carried through four generations the leaves lose

their xerophytie form and structure, but the other charac-

ters are retained within the limits of variability. The

stems show an increase in average length of 1 or 2 em.,

the roots change as much, but the reproductive branches

and floral organs retain their alpine characters. The

slight modifications undergone by these features were

seen to reach a maximum and to decrease in the latest

generations cultivated. The structural changes and im-

plied functional accommodations are indubitably direct

12 THE AMERICAN NATURALIST [Vou. XLV

somatic responses, there is no escape from the conclu-

sion that the impress of the alpine climate on the soma

has been communicated to the germ-plasm directly or

indirectly in such manner as to be transmissible, and the

suggestion lies near that repeated and continued excitation

by climatic factors may have been the essential factor in

such fixation.”

Among the most noteworthy investigations of the fea-

tures of interest in connection with habitat changes are

those being made by the anthropologist in which somatic

calibrations of immigrating races and linguistic studies _

of peoples of known origin, geographical movement, and

established relationship are being used to great advan-

tage. No more fascinating chapters of scientific litera-

ture are to be found than those which delineate the migra-

tory movements, segregation and habital reactions of

Polynesian islanders, of North American Indians, or of

Asiatie peoples, yet their value as actual contributions to

the phase of biology of interest to this society is hardly

recognized. The investigator of problems in anthropol-

ogy has the advantage of dealing with an animal whose

psychology, history, traditions and records are readily

intelligible to him, so that a much wider range of facts

may be brought within the zone of reliability than when

we deal with an organism whose actions, at best, are but

imperfectly understood by us.?

A second series of results of great interest and suggest-

iveness are those which have been obtained in various

laboratories as to the individual modifications in cyclical

activity, functionation and structure of plants and ani-

mals in response to unusual stimuli, or under the influ-

ence of unusual intensities of the common environic com-

ponents. The behavior of organisms in constant illumi-

nation, equable and variable temperatures, salinity, alka-

linity or acidity of the medium, unusual pressures of at-

***Versuche ueber Vererbung erworbener Eigenschaften bei Capsella

— pastoris,’’ ait r. Bot. Zeitschr., Vol. 58: pp. 231-236, 285-288, 1908.

e Boas, F., ‘‘Changes in Bodily Form of Descendants of Immi-

ar The Tmimnigration Committee, Document No. 208, presented to the

61st Congress, 2d Session, Washington, D. C., U. B. A., 1910.

No. 529] ORGANIC RESPONSE 13

mospheric constituents, to unusual compounds and unac-

customed food-material, make up an important propor-

tion of the sum total of information ordinarily classified

as physiology. The morphogenic and accommodative

adjustments presented afford by analysis the best con-

ceptions available as to the nature of the physiologic

activity of organisms.

The experimental results of Stockard with fish eggs

subjected to the action of various chemical substances

are of unusual interest in the present connection. The

eyclopean embryos of Fundulus formed in sea-water con-

taining magnesium salts offer the first known example

of the induction of an abnormality in the vertebrates

occurring in nature, by specific reagents. Suggestion of

a common cause is obvious as it is in the instances in

which similar divergences have been secured in the labo-

ratory with plants. As will be pointed out later, such

analytical tests constitute a very important part of the

procedure in the study of acclimatization results.‘

In very few cases, however, has the permanency or

heritability of the deviations induced been tested, and in

most of such tests the agencies employed might ha

acted upon both soma and germ-plasm, as will be ap-

parent upon an examination of the work of Standfuss,

Fischer, Pictet and Houssey. The work of these older

experimenters has been reviewed so many times that it

will be unnecessary to discuss their results further in the ©

present paper. This was done at the Darwin memorial

meeting in 1908, and quite recently by Bourne in his ad-

dress before Section of Zoology of the British Associa-

tion for the Advancement of Science, at the Sheffield

meeting.”

The present opportunity may well be used to make a

presentation of the results of the last few years obtained

“Stockard, ©. R., ‘‘The Development of Artificially Produced Fish.—

The Cyclopean Embryo,’’ Jour. Exper. Morphology, Vol. 7, No. 2, p. 285,

1909

* Nature, Vol. 84, p. 378, 1910, September 22, 1910.

14 THE AMERICAN NATURALIST [ Vou. XLV

by investigations, using a more perfected technique, and

having the advantage of a keener insight into the real

nature of the problems to be solved.

That the general hypothesis with its corollaries is

being subjected to the most critical examination and that

the assumptions implied in the conception of inheritance

of acquired characters are being put to exact and conclu-

sive tests, is readily apparent when a review is made of

recent and current researches in which living material

from widely separated groups of animals and plants is

being subjected to a variety of nutritive conditions and

climatic agencies. Klebs, who has long been concerned

with the morphogenic reactions of plants, has determined

a series of conditions under which the stages of mycelial

development, asexual zoospore and sexual or oospore

formations in filamentous fungi may be inhibited or var-

iously interchanged. Much more important reactions

were obtained from Sempervivum, the live-forever of tae

garden. In this plant, inflorescences were replaced by sin-

gle flowers by experimental excitation while it was found

the number and arrangement of the floral organs as well

as of the stamens and carpels could be altered. Further-

more, the deviations in question were found to be trans-

missible to the second or third generation in guarded seed-

reproductions.°®

Microorganisms with a short cycle offer peculiarly ad-

vantageous material by reason of their simple reproduc-

tive processes, and also by the fact that it is possible to

control environic factors with exactitude. The volu-

minous literature of bacteriology shows that much at-

tention has been devoted to the building up of characters

by selection, and to the study of the behavior of morpho-

logical divergences occurring in special cultures.

The experiments of Buchanan with Streptoccus lacti-

cus yields the conclusion that phases of fluctuating varia-

tions in the bacteria induced by cultures may not be fixed,

° Alterations in the development and forms of plants as a result of

environment, Proe. Roy. Soe. Lond., Vol. 82, No. B. 559, p. 547, 1910.

No. 529] ORGANIC RESPONSE 15

and are not transmissible, which is in accord with the

main body of evidence upon this point. There are, how-

ever, a number of records of the appearance of definite

qualities or morphological characters in the yeasts,

which were transmissible and permanent. These de-

partures were so striking as to be capable of being re-

garded as mutational, and their origin has been ascribed

to the influence of the environment by experimenters of

notable skill, such as Beijerinck, Winogradsky, Lepesch-

kin, Hansen and Barber. It may be recalled in this con-

nection, that environic responses are generally sudden,

and that the entire range of departure may be made in

a single generation, at most in two or three.’

Pringsheim after a comprehensive review of his own

work and of other available evidence obtained by a study

of accommodations or adaptations of yeasts and bacteria

to unusual temperatures, culture media, and poisons,

concludes that some of these variations are fixed

and transmissible both asexually and by spores, while

others are not. It is not easy to analyze contributions

upon this subject with reference to the differential action

of the exciting agencies upon soma or germ-plasm,

neither is it clear as to the action of the selection in the

experimentation. It is important, however, to note that

the alterations concerned are direct functional responses

to the exciting agencies.’

The researches of Jennings with paramecium deals

with conditions of morphology and physiology not widely

dissimilar from those offered by the bacteria with regard

to the present problems, and his work has been carried

out with an extensiveness and thoroughness impossible

to the worker with more massive and more slowly moving

organisms. Cultures were carried through hundreds of

generations with no progressive action in fluctuating

"For a brief review of this subject see Buchanan, ‘‘Non-inheritance of

impressed variations in Streptoccus lacticus,’’ Journal of Infectious Dis-

eases, Vol. 7, p. 680, 1910.

* Pringsheim, H., ‘‘Die Variablitit niederer Organismen,’’ Berlin, 1910.

16 THE AMERICAN NATURALIST [ Vou. XLV

variability; while the organism as a whole was strongly

resistant to all kinds of environic influences, and actual

alterations were extremely rare. Most of the supposedly

acquired characters disappeared in two or three gener-

ations by fission, although one was followed for twenty-

two generations. The new é¢haracter was borne by only

one of the pair produced by a division, except in rare

instances, and in only one case was there found such

modification as to produce a race bearing the odd char-

acter in which the feature in question was imperfectly

transmitted in series of asexual generations.’

The results of Woltereck with Daphnia offer some-

thing by way of contrast and also serve to illustrate the

necessity for continuation of parallel cultures for the

purpose of comparison of divergent forms and the nor-

mal. The particular group of this crustacean furnish-

ing the experimental material is taken to be very var-

liable, and it was subjected to over-feeding with the im-

mediate result that the variability of the form of the head

appeared to be widened, the size of this structure being

increased. This disappeared when lots from the culture

‘were restored to normal conditions in the earlier stage of

the work. After three or four months of over-feeding,

the form of the head came within narrower limits, and

fewer aberrants were seen, while lots returned to normal

conditions, showed a slower restoration of the original

form of the head. Two years after the cultures were

begun, it was found that the original head form was not

displayed by young restored to normal nutrition condi-

tions, the larger helmet being persistent. It seems

fairly certain that a new genotype resulted from the long-

continued action of the culture medium.

* Jennings, H. $S., ‘‘ Heredity and Variation in the Simplest Organisms,’’

AMER. Nart., Vol. 43, No. 510, June, 1909; and other papers by the same

author.

” <t Weitere experimentelle Untersuchungen ueber Artenveranderung spe-

ziell ueber das Wesen quantitativer Artenunterschiede bei Daphniden,’’

Sonderabdruck a. d. Verhandl. d. Deut. Zool. Gesell., 1909.

No. 529] ORGANIC RESPONSE 17

In the experiments of Sumner mice reared in a warm |

room were found to differ considerably from those reared

in a cold room in the mean length of the tail, foot, and

ear, and the differences were transmitted to the next

generation. The differences may be reasonably desig-

nated as being directly individual and somatic, and as

having been transmitted by the germ-plasm, which was

not subject to the action of various temperatures in the

first instance. The reaction forms have an additional

claim upon our attention, since they are the ones which

distinguish northern and southern races of many animals.

The crucial test of the value of the alterations induced in

the mice is the one applicable to all of the experimenta-

tion on this subject, a test in which two parallel series of

cultures, one under the altered environment and the

other under usual conditions, should be kept going con-

tinuously for a long number of years, lots being with-

drawn from both, from time to time, for long-continued

comparative culture in normal habitat and under other

conditions. Effects due solely to fluctuating variability

may be expected to reach a maximum and minimum

within two or three years, leaving the enduring effects

standing alone, or in such relief as to be capable of ready

calibration."

Kammerer carried out some tests with salamanders

three years ago which have the interest attached to any

attempt to interpret geographic or habitat relations. Sala-

mandra maculosa is viviparous when it lives high in the

mountains and ovo-viparous at lower levels. S. atra

is an alpine form and the larvae are large with very long

gills. When the latter form was kept at unusually high

temperatures the larve produced resembled those of S.

maculosa in its lower warmer habitats. S. maculosa

kept in low temperatures and without water showed a

cumulation of effects by which the characters of the

“ Sumner, F. B., ‘An Experimental Study of Somatie Modifications and

their Reappearance in the Offspring,’’ Archiv. f. Entwickelungsmechanik

d. Organismen, Vol. 30, pt. 2, p. 317, 1910.

<

18 THE AMERICAN NATURALIST [Vou. XLV

young and the reproductive habits resembled those of

S. atra. The conditions of these experiments are not

such as to allow a definite separation of somatic and ger-

minal effects, neither was the permanency of the newly

acquired habits tested to such an extent as to determine

their hereditary value. That characters and habits may

be modified in such manner as to appear in the next gen-

eration or two in the absence of exciting conditions is il- -

lustrated by hundreds of authentic examples in plants

which have long been known.12

My own earlier work with relation to this subject con-

sisted chiefly of ovarial treatments in which the main

and accessory reproductive elements of seed-plants were

subjected to the direct action of solutions of various

kinds. New combinations of characters constituting a

distinct elementary species or genotype were obtained in

one plant, and the divergent type has been found to trans-

mit its qualities in the fullest degree as far as tested, to

the fifth generation. Still more marked forms were ob-

tained in a second genus, the divergent progeny being

lost in transference to the Desert Laboratory, while —

marked responses have been obtained in the extensions

of these experiments upon species representing widely

different morphological types in Arizona. The greater

majority of the tests have been made upon plants grow-

ing under natural conditions, so that environmental reac-

tion in addition to that of the specific reagents might be

excluded. Progenies representing many species, in-

cluding thousands of individuals, many of which are di-

vergent, are now under observation. Absolute finality

of decision with respect to the standing of the new types

may be reached but slowly.

Gager produced chromosomic aberrations in the reduc-

ing divisions of Enothera by irradiations and such excita-

tion was also followed by the appearance of aberrants in

the progeny, the hereditary qualities of which have not

* Arch. f. Entwickel., Vol. 30, pp. 7-51, 1907.

No. 529] ORGANIC RESPONSE 19

been tested. Using similar excitation Morgan induced

the appearance of white eyes and of short wings in a pedi-

gree culture of the fly, Drosophila ampelophila. Both

qualities were sex-limited and mendelized when paired

with the red eyes and long wings of the original type.

Both however seem to be fully transmissible.’

A related phase of the subject is that of the interposi-

tion of environic factors in mutations and hybridizations.

DeVries has repeatedly called attention to the fact that

the composition of hybrid progenies of mutants with

each other and with the parental form might be altered

by nutritive conditions, and the author has cited the fact

that mutations were made by (nothera Lamarckiana

in the climate of New York which had never been seen

in Amsterdam. Furthermore, in discussing the diver-

gent results of DeVries and myself, obtained by crossing

the same forms in Amsterdam and New York, the sug-

gestion was made that ‘‘the manner in which the var-

ious qualities in the two parents are grouped inthe prog-

eny might be capable of a wide range of variation.

Many indications lead to the suggestion that the domi-

nancy and prevalency, latency and recessivity of any

character may be more or less influenced by the condi-

tions attendant upon the hybridization; the operative

factors might include individual qualities as well as ex-

ternal conditions.’’!4

Using abnormal temperatures for excitation, Kammerer

induced color changes in Lacerta constituting female di-

morphism in one species, and male dimorphism in another,

and the newly induced characters, like the original ones,

behave in a mendelian manner in crosses, although the

heredity has not been carried through enough generations

to test their permanence.'®

“ Morgan, T. H., The method of inheritance of two sex- -limited charac-

ters in the same pilak. Proc. Soe. for Exper. Biol. and Med., Vol. 8, No.

1, p. 17, 1910.

yi MacDongal, Vail, Shull and Small, ‘‘ Mutants and Hybrids of the

(Enotheras,’’ Pub. No. 24, p. 57, Gatniele Inst. of Washington, 1905.

Vererbung erzwungener Farbenaenderungen. Arch. f. Entwickl., Vol.

39, Hefte 3 and 4, p. 456, 1910.

20 THE AMERICAN NATURALIST [ Von. XLV

Much more striking evidence upon the matter has been

recently obtained by Tower in intercrossing Leptinotarsa

decemlineata, L. multitineata, L. oblongata and other

species in their habitats in southern Mexico, and at the

desert laboratory. Among other divergences one of the

three first generation intermediates characteristic of

these cultures was lacking from the Tucson cultures,

although two other such forms were included.1* In a

teh i | | | | eo

` lek A ; baa. T.

f,

Fie. 1. Acclimatization shelters and beetle cages, Desert Laboratory

(2,600 ft.).

comprehensive treatment of the entire subject with espe-

cial reference to modifications in dominance Tower says:

The experiments and observations herein given warrant the general

statement that conditions external to a cross are important factors in

determining the results thereof. This conclusion has been worked out

in both normal and hybrid erosses, in crosses between races which

have been created selectively, and between forms which arose as sports;

* See Report, Department of Botanical Research, Carnegie Institution of

Washington, for 1908 and 1909.

No. 529] ORGANIC RESPONSE 21

and the second series of experiments in synthesis is sufficient warrant

for attributing to this factor a considerable importance in evolution.”

Tennent arranged a series of hybridizations of Echino-

derms at Tortugas which yielded data of great interest in

connection with the earlier conclusions of Vernon, Don-

caster, and Herbst as to the influence of temperature and

season changes upon dominance. From the information

derived from crosses of Hipponoë and Toxopneustes it is

clear that the dominance of the parental characters is

dependent upon the alkalinity or the concentration of the

OH ions. The products of the trial cross fertilization,

however, were not reared to maturity.'§

No phase of the subject under discussion is more

readily amenable to experimental investigation, and no

results may be expected to bear more directly on the

mechanism of inheritance than those in which similar

unions give dissimilar progenies under the pressure of

unlike environments. It is to be noted that everything

of value with regard to the influence of environment

upon hybridizations has been secured by the introduc-

tion of the geographic or climatic element, that is, the

unions leading to divergent results have been made in

habitats in which the environic complexes differed not in

one, but in many features. Thus the climatic components.

in southern Mexico reach dissimilar maxima and minima.

and run unlike courses from those of Arizona.

This method of transplantation of organisms to dis-.

tant localities furnishing congeries of climatic factors

markedly different from those of the habitat in which

they were found is one which offers opportunities of the

broadest kind, and such exchanges have been made be-

tween fresh and salt water, cave and surface, alpine

" Tower, W. L., ‘‘The Determination of Dominance and the Modifiea--

tion of Behavior in Alternative (Mendelian) Inheritance, by Conditions:

Surrounding or Incident upon the Germ Cells at Fertilization. (Reprinted:

from Biological Bulletin, Vol. XVIII, No. 6, Ma

sS

eport, Director Dept. of Marine Biology, Carnegie Institution of

Rinshiapton for 1909 and 1910.

22 THE AMERICAN NATURALIST [ Vou. XLV

summits and lowland plains, high and low latitudes,

with results of somewhat limited value until recently.

The first of these in which plants were used was made by

Nägeli, who carried on observational work on a large

number of species in plantations of the botanical garden

at Munich, detecting certain obvious alterations which

did not appear to offer anything of hereditary value.

The more recent work of Bonnier was directed chiefly

toward comparison of the vegetative activity, anatomical

modification, and developmental habit of plants ex-

changed between the mountain and low-land. The care

used in attempting to transport soils with the plant was

almost wholly without direct application, since the char-

acter of the soil is so largely a function of climate that

the course of a single season would suffice to change or

materially modify any transported soil. Such a precau-

tion might have the sole merit of furnishing the trans-

planted species with a limited amount of some compound

necessary for its growth, but any small amount of soil

becomes quickly permeated by solutions from the forma-

tions below and contiguous to it. Bonnier’s results in-

clude much that is suggestive, although no effects were

secured which did not disappear within two or three sea-

sons after a plant had been removed from the influence

of the exciting agencies or returned to its original hab-

itat.

The first realization of results of importance from

cultures widely extended geographically has been ob-

tained in the experiments with Leptinotarse by Tower,

in which various species of these beetles were studied in

their habitats in southern Mexico, in open air and glass

houses as far north as Chicago, as far east as the Atlan-

tic and as far west as the Desert Laboratory. Facilities

for work upon special problems are now being organized

at several places and many contributions to the subject

may be expected within the next decade.

The plan for work upon the problems of special in-

terest in connection with the Department of Botanical

No. 529] ORGANIC RESPONSE 23

Research of the Carnegie Institution of Washington, im-

plies the establishment of experimental cultures in lo-

calities which furnish distinct types of climate, or which

have characteristic complexes of meteoric factors, as in-

dicated by the vegetation indigenous to them. Secondly,

these localities have been chosen with regard to their geo-

graphical relations so far as possible, in order that the

possible and probable fate of migrating species might

be studied. The behavior of plants in these localities is

Fic, 2. Santa Catalina mountains as seen from Des ert Laboratory. Experi-

mental plantations shown in figures 3 and 4 are located on this ra nge.

recorded as to anatomical alteration and physiological

departure. Having detected some such feature of ap-

parent importance, its reappearance in plants from seeds

carried to the original habitat and other locations is fol-

lowed as one line of evaluation. C Jontemporaneously,

the form is taken into the laboratory and here by analy-

tical experimental tests the effort is made to ascertain

to what special agencies the departures are due. Four

24 THE AMERICAN NATURALIST [ Vou. XLV

main locations furnish the chief facilities for these some-

what extensive experiments, which may be briefly charac-

terized as follows. The domain of the Desert Laboratory

has a subtropical arid climate, with one cool moist sea-

son, one warm wet season, two intervening dry seasons,

the vegetation being chiefly composed of spinose xero-

phytic shrubs and woody plants, with a large number of

the more advanced types of desert plants, which carry an

immense water balance, such as the cacti and other suc-

culents. The total rainfall is 12 inches, relative humid-

ity falls as low as 5 per cent. for extended periods and

the soil moisture remains below 10 per cent. for weeks,

and the altitude is 2,300 feet; maximum temperatures of

112°-114°, minima of about 16° F., with a total exposure

below the freezing point of from 12 to 80 hours per

annum are encountered.

The xero-montane plantation lies at 5,400 feet on the

near-by slopes of the Santa Catalina Mountains at the

extreme upper edge of the characteristic desert flora in

the oak belt of vegetation with a rainfall of 16 to 18

inches per year, minima a few degrees lower than those

of the Desert Laboratory, with such an extension of cold

nights as to make temperature a distinct limiting factor;

relative humidity is extremely low, soil moisture quite as

low as that of the base plantation, and the activity of

vegetation of the winter wet season which is such a.

marked feature of the lower plantation is entirely lack-

ing. The meteoric and other agencies carry a constant

stream of seeds from this locality into the region of the

laboratory.

The montane plantation lies at an elevation of 8,000

feet in a forest of pine, spruce and aspen, with a climate

equivalent to that of northern Michigan, the growing

season being about 110 days, the winter being character-

ized by a heavy snowfall and temperatures as much as

20°—25° below zero Fahrenheit. The spring and autumn

are dry, and midsummer has the usual manifestation of

heavy thunder-storms, in which the precipitation is

No. 529] ORGANIC RESPONSE 25

slightly less than the amount in the winter. The yearly

total is between 35 and 40 inches. The vegetation is

characterized by conifers, grasses and a wide variety of

herbaceous and shrubby perennials, very few annuals

being found here. The mountain streams carry the seeds

of the contiguous elevated slopes and valleys in great

profusion to the region of the xero-montane plantations

and to the lowlands of the character of those around the

Desert Laboratory. These three localities form a con-

nected series in which the behavior of the tested species

may be expected to offer phenomena of wide significance

and of direct bearing on many phases of geographical

distribution and evolutionary advance.

The fourth plantation is at Carmel, California, some

800 miles distant in a straight line from the first three,

within a thousand yards of the Pacific Ocean in a forest

of Monterey pine, the soil being granitic sand, with or-

ganic material or humus in some places, and a heavy

cement in others. The climate is characterized by a win-

ter wet season, in which the minima are scarcely below

the freezing point and the exposure to such low tempera-

tures is for not more than fifteen or twenty hours per

year. A period of heavy continued fogs during two

months of the midsummer results in minima of 41° F.

in July and August, there being almost no precipitation

between March and November. The total precipitation is

about 18 inches per annum. The place, therefore, has

one rainy season, a dry spring and fall, and a cool mid-

summer, conditions exceptionally favorable for the sur-

vival of species introduced from the localities of the

other three plantations of the series. It is obvious that

if the data concerning the climatic factors are integrated

or summarized and placed in parallel columns a ready

means is afforded for detecting the causes which prevent

survival or facilitate the development of any form in

any locality, and a proper analysis of the same facts

may also yield direct suggestions as to the nature of the

excitation responsible for any departure on the part of

a plant removed from one habitat to another.

26 THE AMERICAN NATURALIST [Vou. XLV

The groups of species interchanged among the four

different localities include material upon which such

analysis may be most readily made. In addition, the

introductions are also arranged to simulate certain geo-

graphical movements and topographical effects. Spe-

cies from eastern America and from the lower plantations

are taken to the montane and xero-montane plantations

to meet conditions similar to those they might encounter

in a migration toward alpine or arctic regions. Species

from the montane locations and from the eastern states

are carried to the desert plantations to have the expe-

rience of a southward movement, or that of descending

mountain valleys, while all of these localities have fur-

nished forms for establishment in the maritime locality

characterized by equable conditions in which species may

range widely as to latitude and indefinitely as to longitude.

The preliminary exchanges included over a hundred spe-

cies, mostly biennials and perennials; the survivals amount

to less than 80, while perhaps not more than a score of

these may be expected to yield results of value or interest.

Our increased insight into the nature of natural groups

of organisms has shown the necessity and suggested the

means of observing certain distinctions and precautions

in this work. Thus it is of the greatest importance that

the living material shall be shown to be either simple

genotypes or that its phaenotypic nature be apprehended

in order that the integration and combination of these

forms shall not be mistaken for environic effects. When

a lot of plants is taken from one plantation to another,

data of the original locality are preserved as the stand of

the plant in that place serves as the control. If the plant

is multiplied vegetatively in the test, it might reveal a

possible complex character of the material in bud-sports,

but other divergences might be well ascribed to local

effects. On the other hand, if introduced in the form of

seeds, the possible complex character of the material

would soon become apparent, especially if the generations

were followed properly. In the actual.management of

No. 529] ORGANIC RESPONSE AT

the cultures, it is found profitable to re-introduce forms

from the original or control lot of various species in

order to follow the first stages of their adjustment re-

peatedly.

The earlier introductions were made in May, 1906, but

the establishment of the system was not completed until

early in 1909. Some of the species have therefore been

observed through the fourth growing season in newly

encountered habitats, and as the somatic responses are

Fig. 3. Xero-montane plantation (5,500 ft.), Santa Catalina Mts., Arizona.

immediate or nearly so it may be assumed with some con-

fidence that the alterations observed are those which are

to be tested as to their transmissibility. It may be of

interest to note briefly some of the more salient alterations

with some attention to their geographical significance,

reserving the discussion of structural details for a more

suitable occasion.

1. Many species of perennials native to regions in

eastern America with a temperate summer or growing

28 THE AMERICAN NATURALIST [VoL. XLV

season 160-170 days in length, and a winter with ex-

tended exposures below the freezing point, endure the

climate of the montane plantation with lower minima,

shorter growing seasons and more arid dry seasons, all

seasonal changes being much more sudden and pro-

nounced than those encountered in their original habi-

tats. Trillium, Arisema, Roripa, Sanguisorba, Fragaria

and others offer examples of such survival.

2. Perennials as above survive and thrive in the

equable climate of the maritime plantation in which much

more equable conditions are found than in the original

habitats—Podophyllum, Sanguisorba, Arisema, C£no-

thera, Roripa and Fragaria.

It is to be noted that many species of annuals and per-

ennials are supposed to range from the temperate low-

lands of New York to similar montane climates farther

south in the Rocky Mountain region, and also to the Pa-

cific coastal belt. Critical examination of material rep-

resenting the supposed inclusion of the species generally

reveals differences denoting elementary species or geno-

types which might be grouped together in a Linnean

treatment. These relationships offer some most inter-

esting probabilities as to derivation and dissemination

which may not be touched upon here.

3. Species from the montane plantation survive and

show a luxuriant growth in the maritime plantation with

various vegetative modifications, of which Fragaria,

(Enothera, Juglans, Scrophularia, Senecio and Dugaldea

offer illustrations.

4. Species from the montane plantation survive and

show a development somewhat atypic when carried to the

foot of the mountain on which they are indigenous. Ex-

amples are Œnothera, Juglans, Scrophularia and Fra-

garia.

5. Species from the arid region about the Desert Labo-

ratory survive and show atypic activity in the equable

maritime climate. Illustrations are offered by the

Opuntias, Parkinsonia and Penstemon. Species from the

No. 529] ORGANIC RESPONSE 29

equable maritime location do not survive when taken to

any of the other plantations, with the single exception of

Fragaria Californica, the extremes of temperatures

being the evident limiting factor.'®

By the consideration of the responses of plants in the

various climates into which they may be introduced in

these experiments, it is possible to determine with some

accuracy the limiting factors acting for the exclusion of

the form in question. The analysis of the responses to

changed environment may be briefly given as follows:

Species from locations with well-marked seasons, in

which there is a definite contrast between the warm and

dry periods or between dry and rainy seasons, show a

lessened tendency to sexual reproduction, and a conse-

quent weakened capacity to form fruits and seeds when

taken to locations with equable or monotonous conditions.

This is a fact well known to the grower of economic

plants, the chief examples being offered by bush and tree

fruits disseminated to the southward. Fertilization and

the preliminary stages of seed formation may ensue as

usual, but the absence of the stimulating effect of chang-

ing temperatures usually characterizing the close of a

season appears to be followed by a lack of development

of the fruit. Examples of this are offered by Arisema,

Salomona, Sanguisorba, Actea, Podophyllum, Menisper-

mum, Apios Fragaria and Phytolacca. Exceptions are

offered by Senecio, Ginothera (some species), Potentilla,

Geum and others.

The transplantation of a species from one type of cli-

matic complex to another generally alters the shoot-habit,

or pattern of development of buds. The maritime loca-

tion is characterized by a profuse development of run-

ners and offsets, and the growth of branches on the lower

part of main axis, above or below ground. In some spe-

cies, the main axis remains in a very rudimentary condi-

tion. Excellent illustrations are furnished by @nothera,

Scrophularia, Dugaldea and Phytolacca.

See Kuckuck, P., ‘‘Ueber die Eingewéhnung von Pflanzen wirmerer

Zonen auf Helgoland,’’ Bot. Ztg., Vol. 68: 49-86, April, 1910.

30 THE AMERICAN NATURALIST [ Vou. XLV

The removal of the higher types of plants from the

desert conditions with which they articulate, that is, ex-

treme forms with reduced shoots and swollen stems, is

followed by increased development of spines when grown

é

y

A

I

= Hf

Fic. 4. Montane plantation (8,000 ft.), Santa Catalina Mts., Arizona.

under equable conditions, or in climates with greater

water supply as illustrated by Opuntia santa rita and

other ‘‘spineless’’ forms.

No. 529] ORGANIC RESPONSE 31

The removal of plants from localities with well-marked

seasons to equable maritime climates is followed by a

leaf development which may result in the multiplication

of the parts. Fragaria. All introductions in which

the range of climatic conditions to which the plant was

subject was narrowed, were followed by increased vege-

tative activity, which multiplied underground branches

and propagative bodies.

The concurrence of these responses in a single form

may be well demonstrated by the results of studies of a

genotype near Scrophularia leporella, found in the vicin-

ity of the montane plantation, which has survived in the

shade at the Desert Laboratory and at the seaside locality.

In its native habitat, it shows a strict, scarcely branch-

ing shoot with a few fleshy succulent roots, which appar-

ently carry water with a small dissolved content. When

this form is taken to the Desert Laboratory, its repro-

ductive season is lengthened from two months to five or

six months, although but few seeds are formed, the shoots

branch more profusely, and a greater mass of under-

ground members are formed. In the maritime location

these features are accentuated and the development of

branches goes on to such extent that the shoot gives rise

to a number of main branches which can not be supplied

with water, and hence soon wilt and die. The under-

ground system now includes dozens of thickened members

from one to two centimeters in diameter, which may show

a total weight of from 6 to 8 kilograms.

The removals of forms included in the experimental

series may be taken as fairly parallel to the distributional

movements effected by various agencies without the in-

tervention of man. Some, as a matter of fact, are exact

duplicates of occurrences in which these same species

participate. The alterations noted are undoubtedly en-

vironic effects, and may be attributed chiefly to climatic

factors. Two common assumptions as to the behavior of

plants are to be noted when species are removed to local-

ities widely separated from the habitat in which they are

32 THE AMERICAN NATURALIST [ Vou. XLV

found. If they fail to survive or do not flourish in the

second location, they are said to have failed to adapt

themselves to the new conditions. Into this statement

may be read one more in accordance with a physiological

consideration of the matter to the effect that the inten-

sities of some of the factors present exceeded the maxima

of the plants in question and thus acted as limiting fac-

tors to their proper or full development or survival.

The second assumption is to the effect that the altera-

tions displayed by a plant in newly encountered habitats

are adaptive and that these changes render the organism

displaying them better fitted to meet the conditions.

Some reactions are of such a nature as to be of benefit

to the plant displaying them, but the worker who assumes

that this is true of all changes even in species which

thrive and luxuriate in the new habitats will soon find

himself widely afield from facts capable of being substan-

tiated by experiments. Thus in the case of the Scrophu-

laria noted above, the new maritime habitat includes a

congerie of agencies which incite it to form enormous

clusters of thickened roots and to exhibit the habit of

branching densely. So many branches are formed in fact

that the conducting channels at the base of the shoot

are incapable of carrying a supply of water adequate to

the transpiratory needs of the foliar organs, although the

vastly increased balance in the root-system would be suf-

ficient to meet the needs of the plant for days, and con-

sequently the widely spreading shoots of these plants

show a large proportion of branches which have about

reached maturity and are dying. The behavior of the

semi-spineless opuntia (O. santa rita) offers illustration

of the same sort. Bearing only a few or no spines in

its native mountains, the new segments in the cool

foggy climate of Carmel are spinose at almost every

areole. Here the result is very plainly one of the awak-

ening of a latency, since it seems fairly clear that this

plant and all of its relatives show spines as a final stage

in the reduction of the shoot system, and that the spine-

less form is the culmination of a line of progress. The

No. 529] ORGANIC RESPONSE 33

reappearance of the spines is, therefore, one of regres-

sion; in a paper before this society a year ago I was

able to present results of experimental parasitism, in

which the reactions of autophytic green plants when

grown as parasites included a number of phenomena,

which were not only not adaptive in any sense, but which

might reasonably be considered as distinctly unsuitable.

Among these was included the very striking autonomic

movements of etiolated segments of the prickly pear

(Opuntia) when it was led to fasten upon other plants as

- a parasite.”

Many alterations in plants in the cultures, however,

particularly those concerning the reproductive habits,

may readily be interpreted as being adjustments of a

directly adaptive character. With these are many cor-

relative changes which are simply carried along. It

seems fairly certain that the distinction between the pri-

mary adjustive alterations and correlative effects will

be made clearer in any analyses made of the possibil-

ities of inheritance of somatic changes. In connec-

tion with the discussion of the nature of the parasitic

adjustments the behavior of a drop of water when rest-

ing upon a rough surface was offered as an illustration

of the modifications of an organism under environ-

mental influences. The sectors of the drop in direct

contact with a hard object which is not wetted will

be most markedly and directly altered, in a manner

parallel to the reactions in functions most directly af-

fected by environment, while the free sectors or qualities

of the drop or of the organism will be altered in various

degrees by correlation stresses.

So far as the responses in the cultures at the four plan-

tations are concerned, they appear to the fullest extent at

once and in the first generation. Whether any of them may

become fixed and transmissible in a long series of genera-

tions subjected to the same conditions, like Daphnia, re-

mains to be determined. That this might be the most

* MacDougal and ‘Cannon, ‘‘The Conditions of Parasitism in Plants,’’

Pub. No. 29, Carnegie Institution of Washington, 1910, p. 37.

34 THE AMERICAN NATURALIST [ Vou. XLV

important feature of all experiments of this kind was

pointed out three years ago.™ Although our attention

has been focused chiefly on the possibilities of the trans-

mission of somatic effects by seed reproduction, yet it is

to be recalled that the continuation of an alteration by

fissions, division or cuttings might come to have great

biological significance.

Fig. 5. Maritime plantation near the sea-shore, Carurel, California.

Jennings would consider the Paramecia as free germ

cells subject to the direct action of environment, and

themselves propagating by simple division if his meaning

is properly apprehended. If this is allowable, the same

conception may be extended to include cuttings and all

fission methods of reproduction in plants, even of the

most advanced types. Asa general rule, when a portion

of the sporophyte of a plant, such as an offset, runner,

stolon, tuber, bulb, corm or other detached branch pro-

duces a new individual, the mature characters of the par-

ent disappear in the regeneration or sprouting and the

“<< Fifty Years of Darwinism,’’ 1909.

No. 529] ORGANIC RESPONSE 30

ontogenetic procedure of the plantlet will be much like

that of a seedling.

The exact observation of the manner in which environic

effects may pass the regeneration stage and reappear

has not yet been made to any great extent. Doubtless

many conditions will be found to affect the process.

Bud sports, or vegetative mutations, are, of course, fully

transmissible along a series of stages of division by

cuttings, and many of them have been found to trans-

mit their divergent characters by seed resulting from

close pollination. Mechanically considered, the vegeta-

tive reproduction of a plant consists simply of its per-

petuation through an unbroken chain of metameres or

internodes, each joint arising from a growing point borne

terminally or laterally by its predecessor. The projec-

tion of induced characters formed by metamere A into

metamere P, therefore, involves the question of germ-

plasm as represented by the embryonic mass of the grow-

ing points with no opportunity for carrying over struc-

tures mechanically as in the Paramecium. The compar-

ative action in heredity when plants are transported to

new climates through bulbs and tubers and through seeds

is one that has not yet been made, although doubtless hor-

ticultural and agricultural literature is rich in the records:

of facts upon which decisive generalizations might be

made.

The genetic character of environic effects remains to

be considered. In any species or genotype there is,

withal, a limited number of things included within the

morphological possibilities. The appearance of any char-

acter in an acclimatization culture raises a question

at once as to the standing of the new feature. Is it a

regressive character, once displayed by the species and

now recalled by the very conditions under which it was

first induced, or is it to be considered as a character de

novo, arising simply and directly in response to the ex-

ternal agencies which have been seen to induce it? Thus.

in the results cited above, our general knowledge of the-

Cactacee leads us to assert with some confidence that the.

reappearance of a full complement of spines in a prickly

36 THE AMERICAN NATURALIST [ Vou. XLV

pear from which they had all but disappeared is a regres-

sion or return to the condition of the greater majority of

the group, a condition which must have been shared by

its ancestors at no remote stage in its progressive

development.

None of the attempts hitherto made to perfect a theo-

retical conception which would be useful in interpreting

the mechanism of environic responses have had anything

more than the most limited usefulness. The stimuli of

climatic and many other agencies do not imply the intro-

duction of any strange or new substances into the bodies

of the organs affected. These agencies might change the

dissociations in such a manner as to modify the relative

number of free ions and thus alter the molecular complex

of the living matter in a very important manner. The

intricate play of enzymatic action might also be altered,

and any modification of the relative reaction velocities of

the more important processes might result in material

and permanent change, especially in those cases in which

external agencies interfere directly with the action of the

germ-plasm.

The introduction of solutions into ovaries or the ex-

posure of reproductive elements to unusual irradiation

may raise the additional liability of disturbed polarity

and of modified surface tensions in the cells. It is conceiv-

able that the rearrangement or disturbance of the local-

izations of substances, especially the mineral salts, might

seriously modify the capacities of the bearers of heredity.

These direct and material possibilities offer an adequate

basis for the organization of experimental research upon

the main subject, as well as the means of interpretation

of results without recourse to schemes of particulate

inheritance or theories as to the constitution of germ-

plasm to which may be ascribed usefulness in the discus-

sion of other problems in evolution.

The theoretical consideration of the subject which seeks

to assign all cases of inheritance of environic effects to

the direct action of the existing agency upon the germ-

plasm in itself is one to be regarded with some wariness,

as it may lead us into empiric assumptions which may

No. 529] ORGANIC RESPONSE st

conceal rather than visualize the actual occurrences.

Direct germinal effects are undoubtedly secured in ovarial

treatments, and Tower’s analytical cultures showed that

certain somatic characters induced directly might be

secured also by direct excitation of the egg. Such con-

currence of reaction may be expected especially with re-

gard to some qualities of simpler organization. Not so

readily -interpreted are the responses of Sempervivum.

Alterations in size, number, and structure of floral organs

brought about by excitation during ontogeny are surely

not coordinate with changes in the germ plasm induced

simultaneously. In the ease of Capsella the transference

to an alpine habitat of the plant in the shape of seeds is

followed by immediate and direct ontogenetic alterations

affecting a multitude of characters. Not until these so-

matic responses have been repeated, dozens, scores, or per-

haps hundreds of times, is an impression made on the

germ-plasm that allows it to carry the new characters in

the absence of the inducing. These facts suggest to us

that the soma is in the closest association with the germ-

plasm, has both theoretical and actual qualities different

from it, and any changes in these must inevitably be com-

municated, by the action of hormones or other physio-

logical mechanisms.

A brief paraphrase of the foregoing discussion may be

useful in emphasizing some of the more important mat-

ters which have been touched upon. It is readily appar-

ent that the assumption of the inheritance of acquired

characters, after a long period of tolerance, with but

little research activity bearing upon its principal claims,

is coming in for a large share of attention from the ex-

perimentalist, and there seems a fair prospect that de-

cisive facts may be obtained within a period, very brief

in comparison with the century since the principal tenets

of the theory were first formulated. Already results are

available which have been obtained by cultures of animals

from paramoecia to mammals, and of plants from bacteria

to the higher seed-plants.

_A critical consideration of the available information

seems to justify the following generalizations:

38 THE AMERICAN NATURALIST [Vou. XLV

External agencies acting upon bacteria, crustaceans,

beetles, fungi, and some of the higher types of seed plants

have been seen to result in the appearance of new types

or genotypes, which have been found to transmit their

characters perfectly through so many generations as to

indicate practical permanency.

In the greater majority of such cases of changes in

heredity, inclusive of Tower’s cultures of beetles, Wol-

tereck’s experiments with Daphnia, Morgan’s results with

flies, and my own ovarial treatments of seed plants the

germ-plasm was exposed to the excitation of unusual cli-

matic factors, irradiation, concentrated nutritive media,

or of solutions of sugar or inorganic salts.

The new qualities were seen to be fully displayed, and

to appear in a mutational manner in all of these in-

stances, although the new head form acquired by Daphnia

in Woltereck’s experiments did not become fixed and

fully heritable until the organism had been kept under

the influence of the exciting agency for an extended period,

nearly two years. The most recent and one of the most

interesting series of results are those which show that

the influence of environic factors upon hybridizations

by excitation of the germ-plasm may alter materially

the results of the unions of identical pairs. This seems

- to have been first suggested by De Vries and to have

been seen by MacDougal in hybrids of mutants of Gino-

thera, while it has been established beyond doubt by the

extensive and conclusive results of Tower in crossing

beetles under various conditions that environic agencies

may exert a very marked effect upon the dominancy of

paired characters and the general composition of hybrid

progenies. A different phase of the matter is represented

by the experiments of Kammerer, in which, characters

constituting temporary sexual dimorphism mendelize

when paired. Aberrants, sports or mutants have been

seen to arise and perpetuate themselves under unusual

culture conditions in yeasts and bacteria, their survival

being dependent upon pedigreed cultures in some cases;

and the successive generations were those resulting from

fissions, although in some cases spores were interposed.

No. 529] ORGANIC RESPONSE 39

Many of the purely accommodative adjustments dis-

played by these organisms and by Paramecia as well as

the extremes of variability induced by external agencies

and continued by selection, do not become fixed and are

not transmissible even in a series of generations by fis-

sion. The recent work of Pringsheim, however, shows

that some alterations in the way of accommodations or

functional responses of yeasts and bacteria to unusual

temperatures, culture media, and toxic substances become

fixed and transmissible both by fission and through

spores. It is not clear, however, that the differential

action of the exciting agent upon soma and germ can be

made out, and perhaps nothing more definite might be

said than that both are directly and simultaneously ex-

posed and exhibit coincident reaction.

When we pass to a consideration of the results of Zed-

erbauer and Klebs, however, the evidence becomes much

more decisive. A Capsella was found growing at an ele-

vation of 2,000 to 2,400 meters in Asia Minor which had

hairy stems, 2-4 em. long xerophytic leaves, and reddish

flowers. This plant had been evidently introduced from |

the lowlands by man along a route that has been in use

for more than 2,000 years. The Capsella of the lower

plains forms a stem 30-40 em. high, has whitish flowers

and broad leaves; when its seeds are taken to elevations

with climates comparable to the above, individuals are

developed duplicating those of the highlands,. so that the

characteristic features of this alpine form are clearly

direct somatic reactions; and that they have become

fixed and fully transmissible is demonstrated by the fact

that in a series of generations grown at lower levels the

stem characters, as well as those of the reproductive

branches and floral organs, retained their alpine acquired

characters, although the leaves, as might be expected,

returned to a mesophytie form with broad lamine.

The results obtained by Klebs include divergences of

stem habit, number and structure of floral organs in

Bompervsdi which are not capable of being interpreted

as functional or adaptive responses to the agencies which

called them out and were found to be fully transmissible

40 THE AMERICAN NATURALIST [ Vou. XLV

by seeds, in which case it is fairly clear that somatically

produced characters have been impressed upon the germ-

plasm and carried by it to succeeding generations. The

structural and functional features displayed by Semper-

vivum in these laboratory experiments are not adaptive

in any sense in contrast with those of Capsella, which are

direct responses.

The actual transplantation of organisms from one lo-

cality to another, as a method of experimentation, prom-

ises the results of highest value and widest significance,

especially when taken in connection with analytical lab-

oratory cultures. This method of approach is one which

may yield evidence of the greatest value upon the influ-

ence of isolation and other geographical factors, but is

also one which allows the repetitive or mnemonic effects

to be evaluated. When supplemented by laboratory

analyses and cultures to determine the nature of altera-

tions induced, such methods promise results of the great-

est value. A series of plantations including locations from

mountain tops to the seashore has been established in con-

nection with the Desert Laboratory in accordance with this

idea, and in addition to the interchange of species from

the various localities a number of introductions have

been made from eastern America. Negative or positive

results of sufficient inclusiveness to permit analyses as to

the nature of the exciting agency and the permanence of

the response are yet available.

Some of the characters called out by environic agencies

may be retracements, or regressions, as the reappearance

of spines in cacti, or they may be awakened latencies or

organizations de novo. Some of the responses may result

in sexual dimorphism, while in others the induced char-

acters may be sex-limited. The alterations induced by

external agencies may be cumulative or mutative as to

appearance or organization, and they may be permanent

upon first appearance, or on the other hand may need

generations of repetition before becoming fixed. And

lastly the changes may be orthogenetie or heterogenetic

as to direction, adaptive and accommodative or correla-

tive, or wholly inutile as to their functional relations.

THE NATURE OF GRAFT-HYBRIDS

PROFESSOR DOUGLAS HOUGHTON CAMPBELL

STANFORD UNIVERSITY

Tue possibility of hybrids arising as the result of

grafting long has been a mooted point and the subject has

given rise to much discussion.

The history of the small number of graft-hybrids that

have hitherto been recorded is small and is not as com-

plete as might be wished; indeed it has been claimed re-

peatedly that these supposed graft-hybrids are not really

such but have been produced by the ordinary method of

cross-fertilization. The most famous of these graft-

hybrids is the much discussed Cytisus Adami which

originated at Vitry near Paris about 1826. This was

said to have been the result of grafting Cytisus pur-

pureus upon C. laburnum. A series of supposed graft-

hybrids is also recorded resulting from grafts between a

thorn, Crategus monogyna, and the medlar, Mespilus

germanicus. Three of these graft-hybrids were secured

hy Bronvaux. The hybrids in this case were not all alike

and were given special names and the genus Cratego-

mespilus was proposed for these bi-generic hybrids.

Of the recent opponents of the graft-hybrid theory the

best known is the distinguished botanist Professor E.

Strasburger, of Bonn. Strasburger made a careful cyto-

logical study of Cytisus Adami which has been retained

in cultivation ever since its origin some eighty-five years

ago. Strasburger came to the conclusion that Cytisus

Adami was a real sexual hybrid and not a graft hybrid.

He believes that if the latter were true the nuclei of the

hybrid would show a double number of chromosomes.

This, of course, implies that in hybrids arising otherwise

than sexually, assuming that a nuclear fusion would pre-

cede the formation of such a hybrid, there would be no

41

42 THE AMERICAN NATURALIST [ Vou. XLV

reduction division of the nuclei comparable to that which

normally occurs before the fusion of the sexual cells in

normal fertilization.

mani ihn

Je

auey ree ius We!

anniari

Fic. 1. A, seedling of the black nightshade, Solanum nigrum ; B, seedling of a

tomato, S. lycopersicum ; O, shoot of the graft-hybrid, S. tubingense; D, E, leaves

of the graft-hybrid, 8S. proteus. (All figures after Winkler.)

Němec,! however, believes that a reduction division

does occur, and there is, therefore, no reason to expect

1 Němec, B., ‘‘Zur Mikrochemie der Chromosomen,’’ Ber. der deutsch.

Botan. Gesellsch., 27, 46, 1909.

No. 529] THE NATURE OF GRAFT-HYBRIDS 43

an increase in the number of chromosomes in the cells of

the hybrid. If such a reduction does occur Cytisus

Adami would show the same number of chromosomes as

C. laburnum which has the same number as C. purpureus.

The study of graft-hybrids has assumed a new interest

through the very important recent investigations of Pro-

fessor H. Winkler, of Tübingen. These investigations

prove beyond question that graft hybrids are possible,

and the numerous experiments carried out with every

possible precaution and showing remarkable ingenuity

as well, furnish by far the most important study on the

nature and origin of graft-hybrids that has yet been pub-

lished. These experiments are being further developed

by Professor Winkler but the results already obtained

are of the greatest interest and value.”

The fact that hybrids may arise as a result of grafting

touches some of the fundamental problems of heredity.

and this makes these papers of Professor Winkler of the

highest importance to all students of heredity, and they

deserve much wider attention than they have as yet re-

ceived.

The plants chosen by Winkler for his experiments were

the black nightshade, Solanum nigrum, and two varieties

of the tomato, Solanum lycopersicum. These two species

are very distinct, and indeed many botanists regard the

tomato as belonging to a distinct genus Lycopersicum, so

that Winkler’s graft-hybrids might be regarded as bi-

generic like the Cratego-mespilus graft-hybrids.

The methods by which Winkler secured his graft-hy-

brids were extremely ingenious. Seedlings of the night-

*1. ‘‘Uber Propfbastarde und pflanzliche Chimeren,’’ Ber. d. deutsch.

botan. Gesellsch., 25, 568-576, 1907.

“Solanum tubingense, ein echter Propfbastard zwischen Tomate und

Nachtschatten, ’? ibid., 27, 595-608, 1908.

3. ‘Weitere oo über Propfbastarde,’’ Zeitschr. fiir Bo-

tanik, 1, 315-345,

4. ‘‘ Uber die ein E der Solanum- eee und die

pig seagrass ihrer Keimzellen,’’ ibid., 8, 190

5.

r Propfbastarde TAR roa “Mittheilung). z

Ber. der deutsch. botan. Gesellsch., 28, 116-118, 1910.

44 ` THE AMERICAN NATURALIST [Vou. XLV

shade and of the tomato were decapitated and reciprocal

grafts were made. In making these unions the graft was

cut either wedge-shaped or saddle-shaped at the point of

junction with the stock. The graft and stock united

readily whether the nightshade or tomato was used as the

stock. After the union was complete the plant was again

decapitated, the cut being made through the region where

the union had taken place. The cut surface thus exposed

is composed of tissue derived from the two members of

the union and from this cut surface a callus soon develops

from which numerous adventitious buds quickly arise.

It was thought that from some of these adventitious buds

arising at the point of the junction of the graft and stock

there might be produced shoots which would combine the

characteristics of the two, or at least might be composed

of tissue derived from the two parents.

Naturally the great majority of the shoots arising

from the cut surface of the stem were either pure night-

shade or pure tomato. But finally shoots were observed

which were evidently of mixed origin. The first of these

graft-hybrids were obviously composed of pure elements

derived from the two parents. Some of these shoots

were almost equally divided by a median line on one side

of which the organs—stem, leaf, ete.—were those of the

nightshade, while on the other the organs were evidently

derived from the tomato. Sometimes a leaf was nearly

equally divided. In most cases one or the other of the

parents predominated, but there was no intermediate

region between the two kinds of tissues and organs. It

is clear that such monstrous forms, for which Winkler

proposes the name ‘‘chimera,’’ are not hybrids in any

true sense of the word, but have arisen from buds in

which there was a mere mechanical coalescence of tissue

from the two parent forms at the junction of the stock

and graft.

Further experiments, however, resulted in the produc-

tion of shoots in which the characteristics of the two

parents were so intimately combined, that their discov-

No. 529] THE NATURE OF GRAFT-HYBRIDS 45

erer felt warranted in assuming that these were really

hybrids, probably arising from the actual fusion of cells

derived respectively from the nightshade and the tomato,

this fusion taking place where the graft had united with

the stock. This cell-fusion was assumed to involve a

fusion of the nuclei as well, analogous to the fusion of the

egg-nucleus with the generative nucleus of the pollen

tube in normal fertilization.

Several types of these graft-hybrids were produced

and to these specific names were given.

The first genuine graft-hybrid was called Solanum

tubingense and it has since been produced several times

and has been propagated by cuttings and distributed to

various botanical gardens. During the past summer I

had an opportunity of seeing this graft-hybrid growing

well in the botanical gardens of the University of Munich.

Solanum tubingense is intermediate in external appear-

ance between the nightshade and tomato but is rather

nearer the former (see Fig. 1, C). The nightshade (A)

has simple, smooth-edged, oval leaves and an almost

smooth stem. The tomato (B) has compound leaves with

sharply serrate leaflets and all of the varieties are

strongly hairy. The hybrid (see Fig. 1, C) has simple

leaves but they are sharply serrate or often slightly lobed

like the leaflets of the tomato, and both stem and leaves

are abundantly provided with hairs.

The flower in Solanum tubingense is also intermediate

in character. The nightshade has small white flowers

with a smooth calyx whose lobes are very short. The

flower of the tomato is much larger, bright yellow in

color and the lobes of the calyx are hairy and very much

longer than those in the nightshade: The hybrid has

flowers which are intermediate in character. They are

larger than those of the nightshade but much smaller

than those of the tomato, but like the latter the flowers

are a pronounced yellow. The calyx lobes are two or

three times as long as those of the nightshade but much

shorter than those of the tomato. Like the latter, how-

46 THE AMERICAN NATURALIST [Von. XLV

ever, there are numerous hairs upon the calyx lobes

which in the nightshade are almost smooth.

The fruit of Solanum tubingense is very much like that

of the nightshade but is rather larger, and although it is

black in color there are some traces of the red or yellow

color of the tomato.

Four other well-marked graft-hybrids were secured

to which were given the names Solanum proteus, Sola-

num darwinianum, Solanum koelreuterianum and Sola-

num gaertnerianum.

The first of these originated in a most peculiar fash-

ion. A chimera was obtained which consisted of two

hybrid components. One of these was the before men-

tioned S. tubingense while the other was a hybrid which

was more like the tomato. This chimera soon divided

into two branches one of which was pure S. tubingense

and the other the new hybrid, S. proteus. The latter

was then removed and rooted and further propagated

by cuttings. This species has very variable leaves (see

Fig. 1, D, E) which on the whole are more divided than

those of S. tubingense, while in the characters of the

flower and the fruit it is more like the tomato than like

the nightshade.

Both of the forms S. koelreuterianum and S. gaert-

nerianum were produced more than once and they are

respectively more like the tomato and nightshade but

each differs in important particulars from either of the

parents.

The form, however, which is of the greatest interest

is the hybrid to which Winkler gave the name 9. darwini-

anum, the third to result from his experiments. This

hybrid arose in a quite different manner from the others

and great ingenuity was shown in isolating and prop-

agating it. The shoot from which this hybrid originated

was a chimera which developed from a graft of a tomato

upon a nightshade. This chimera was made up princi-

pally of pure Solanum nigrum, but a small portion of

it consisted of tissue which was different from any

No. 529] THE NATURE OF GRAFT-HYBRIDS 47

of the forms which had yet been discovered. The

chimera instead of being made up of two portions united

longitudinally was composed mainly of tissue evidently

of pure Solanum nigrum origin. A small strip, however,

near its base was of a different character. This region

consisted of a single leaf, and a small amount of tissue

lying below belonging to the stem. The same form was

secured a second time where it developed from a five-

fold chimera derived from S. proteus. Unfortunately,

it was not possible to propagate this second specimen.

In order to isolate this new form it was necessary to

cause the axillary bud belonging to the single leaf to

develop into a shoot. This was finally successful after

four decapitations of the Solanum nigrum shoot above

it. The final result was a branch which was very dif-

ferent from any of the previously developed forms and

it was named Solanum darwinianum. The point of spe-

cial interest in connection with this form is that of all

graft-hybrids which Winkler secured, this seems to be

the only one which is likely to prove a hybrid in the

strict sense of the word. This point, however, will be

brought out later in the discussion of the real nature of

these graft-hybrids.

All of the hybrids were propagated further by cut-

tings and with the single exception of Solanum koel-

reuterianum, were made to produce ripe fruit which in

all cases was more or less intermediate in character be-

tween the fruit of the nightshade and the tomato. In

Solanum darwinianum, however, the fruit was all sterile

and no perfect seeds were formed. The fruit itself is a

small round berry like the fruit of the nightshade in

form, but having the color and structure of the tomato.

In Solanum koelreuterianum the young fruit set but

failed to reach maturity.

Of the hybrids Solanum tubingense is the most fertile

and produces fruit very abundantly. A considerable

number of the fruits, however, are sterile or ‘‘partheno-

carpic’’ and the seeds in no cases reach their full de-

48 THE AMERICAN NATURALIST [Vou. XLV

velopment. Nevertheless Winkler was able to make

these seeds germinate and the second generation of the

plants was reared. S. gaertnerianum produces fruit only

in small numbers but the seeds are perfectly developed

and germinate readily, the same being true of S. proteus.

REVERSIONS

Winkler observed a number of cases where the graft-

hybrid reverted to one or other of the parent forms.

Similar cases of reversions have been recorded for

Cytisus Adami and Cratego-mespilus. These rever-

sions were studied with special care in his first hybrid

S. tubingense. In several instances where the plant was

cut off below the first lateral bud numerous adventitious

shoots arose from the cut surface, and while some of

these were pure S. tubingense, others were pure Solanum

nigrum, the parent species which is nearer to S. tubin-

gense. In a similar manner S. proteus was observed

frequently to revert to the tomato, but in no case was

there reversion to the nightshade.

Sometimes spontaneous reversions occur. Thus in S.

tubingense the apex of a plant was noted which had sud-

denly assumed the characters of S. nigrum. Winkler

gives an excellent photograph of this plant. In other

cases shoots of mixed nature were seen, some having the

structure of chimeras, half nightshade and half the

hybrid form. In these mixed shoots the inflorescence

had flowers of two sorts belonging respectively to the

nightshade and to the hybrid. Similar mixed inflores-

cences have also been observed in Cytisus Adami.

The Second Generation

In S. proteus and S. gaertnerianum perfect seed is de-

veloped and germinates readily. S. tubingense which

sets fruit freely never has the seed fully developed but

as we have already stated Winkler succeeded in germi-

nating these seeds and rearing plants from them. He

No. 529] THE NATURE OF GRAFT-HYBRIDS 49

explains the failure of the seeds to develop fully to the

fact that the fruit of the hybrid, which closely resembles

that of the nightshade, ripens before the seeds have had

time to complete their development. The tomato fruit

requires a very much longer time for maturing than does

the berry of the nightshade and a correspondingly

longer time is needed for the seed to be perfected; and

he thinks that the longer time required for the seed de-

velopment in S. tubingense is an inheritance from the

tomato parent, while the fruit is mainly of nightshade

derivation.

All of the seedlings derived from these hybrids re-

verted absolutely to that parent form which the hybrid

more nearly resembles. Thus the seedlings of S. tubin-

gense and S. gaertnerianum are pure S. nigrum, those

of S. proteus pure tomate. This behavior also corre-

sponds to that of the very few cases where seedlings

have been secured from Cytisus Adami, these in all cases

proving to be pure Cytisus laburnum.

Of the Crategus-mespilus hybrids only one, Cratego-

mespilus asniéresi produced seed capable of germina-

ting. These seedlings were not reared to maturity but

so far as could be judged from the young plants, were

pure Crategus monogyna, the parent which the hybrid

more nearly resembled.*

The third and fourth generations of the S. tubingense

seedlings retain perfectly the characters of S. nigrum

and the same is the case when they are cross-pollinated

by S. nigrum. Attempts to cross S. tubingense with the

tomato resulted in the formation of fruit but no seeds

were developed. It may be also recorded that crosses

between the two parent forms, the nightshade and the

tomato, were without any result.

S. proteus crossed with the two parent forms produced

seed when crossed with the tomato to which it stands the

nearer, and sterile fruit when crossed with S. nigrum.

* Noll, F., ‘‘ Die Propfbastarde von Bronvaux,’’ Sitzungsber. der nieder-

rheinische Geselisch. fiir Natur- und Heilkunde, 1905.

50 THE AMERICAN NATURALIST [ Vou. XLV

As yet no seed has been obtained from crosses between

the graft-hybrids themselves.

The Nature of Graft-Hybrids

Winkler concluded at first that all the graft hybrids

except the chimeras probably arose from actual cell

fusion and might be compared directly with hybrids

arising from true fertilizations. It was suggested by

another student of graft-hybrids, Bauer,* that these ap-

parent true hybrids might also be chimeras of a type

which he has called ‘‘periclinal,’’ i. e., the outer tissues

are derived from one parent, and the inner tissues from

the other, but none of the tissues themselves are of

hybrid nature. This hypothesis seemed the more prob-

able from the results of investigations of MacFarlane

upon Cytisus Adami in which he showed that the epi-

dermal tissues were strikingly like those of C. purpureus

while the inner tissues were like those of C. laburnum.

An investigation of the Cratego-mespilus hybrids re-

vealed a similar state of affairs.

Acting on this suggestion Winkler made a careful cyto-

logical study of his hybrids and found that four of them

were indeed periclinal chimeras. But one of them

seemed to be a real hybrid resulting apparently from a

fusion of cells at the junction of the graft and stock.

The nuclei in the nightshade and the tomato differ

very much in the number of the chromosomes so that the

determination of the origin of the tissues in the hybrid

is made comparatively easy. The chromosome number

in the sporophytic tissue is twenty-four in the tomato

and seventy-two in the nightshade. These numbers

were found in the tissues of all of the graft hybrids ex-

cept S. darwinianum where the reduced number of the

* Bauer, Erwin, ‘‘ Propfbastarde,’’ Biologisches Centralblatt, 33, No. 1

497-514, 1910.

ë MacFarlane, J. M., ‘‘A Comparison of the Minute Structures of Plant

Hybrids with those ot. their Parents, and its Bearing on Biological Prob-

lems,’’ Trans. Roy. Soc. of Edinburgh, 37, 203-286, 1895.

No. 529] THE NATURE OF GRAFT-HYBRIDS 51

chromosomes in the germ cells was found to be twenty-

four, which was to be expected if these were derived

from cells with forty-eight chromosomes; i. e., one-half

the number of the twenty-four plus seventy-two chromo-

somes of the two parents. It is assumed by Winkler

that a reduction in the number of chromosomes follows

the fusion of the cells. He says:

This chromosome number, i. e., forty-eight, is most readily explained

by the assumption that in the formation of the graft hybrid a night-

shade cell (with seventy-two chromosomes in its nucleus) and a tomato

cell (with twenty-four chromosomes) united. The resulting cell, from

which the subepidermal layer at the apex of the darwinianum hybri

arose, had a nucleus with ninety-six chromosomes which then under-

went a reduction division resulting in forty-eight chromosomes.

This study of the tissues of S. darwinianum indicates

that the subepidermal tissue from which the sporogen-

ous cells develop is of genuine hybrid nature arising

from a fusion of cells including the nuclei derived from

the two parent forms.

In his latest paper (5) Winkler gives a brief summary

of his conclusions which are as follows:

Hybrids may be arranged in two groups, sexual and graft hybrids.

The latter may be divided into three classes S to the theoretical

possibility of their method of origin, viz.: (1) Fusion graft-hybrids

arising from a fusion of two somatie cells ried from distinct species.

(2) “Influenced” (“ Beeinflussungs Propfbastarde”) graft-hybrids

‘which arise from specifie influences of one graft component upon the

other without cell fusion (as through chemical substances, transloca-

tion of cytoplasm, ete.). (3) Chimeras, in which specifically pure

cells from both graft components are combined to form a new individ-

ual. These chimeras may be: (a) Sectorial chimeras in which the two

sorts of cells in the growing point are divided by a longitudinal plane.

(b) Periclinal chimeras in which the periclinal cell layers of the grow-

ing point are furnished respectively from one or the other parent form.

(c) Hyperehimeras in which the growing point is made up of a

mosaic of cells derived from the two parent forms.

The first of Winkler’s graft-hybrids were unmistak-

ably chimeras of the first type. Of his later graft-

hybrids to which he gave special names, all except S.

52 THE AMERICAN NATURALIST [Vou. XLV

darwinianum are periclinal chimeras. This is true also

of Cytisus Adami and the Cratego-mespilus hybrids,

Thus S. tubingense has its epidermal region derived

from the tomato while the inner tissues including those

which give rise to the sporogenous cells are of night-

shade origin. In S. proteus the reverse is the case.

This explains all cases of reversion to the parent forms

and also the character of the seedlings which in the one

case are pure nightshade and in the other tomato, this

being due to the fact that the spores (pollen spores and

embryo-saes) arise from sub-epidermal tissues derived

from the nightshade or the tomato as the case may be.

These remarkable experiments of Winkler’s must be

of the greatest interest to all students of the problems

of heredity. They emphasize a fact, too often over-

looked, that it is not always safe to apply to the study of

plants the data of zoolegy. It must be remembered that

in the evolution of the higher plants there has been a

constant tendency toward a reduction of the sexual re-

productive parts. Many biologists quite ignore the fact

that the flowering plant, as it is generally understood,

is a purely sexless organism. The so-called sex organs,

stamens and carpels, are not such at all, but are non-

sexual sporophylls.

The sexual generation of the highest seed plant is a

far simpler organism than that of the moss or fern and

the sex organs are correspondingly simpler. Moreover

the development of the sex cells and the extraordinary

correspondences in nuclear structure, the reduction

divisions and the mechanics of fertilization must have

developed quite independently of these phenomena in

animal cells, since the two great divisions of organisms,

plants and animals, parted company for good long be-

fore the elaborate structures found in the higher mem-

bers of the two series were developed. Hence it by no ©

means follows that what is true in cne case must neces-

sarily follow in the other.

With the subordination of the sexual generation of

No. 529] THE NATURE OF GRAFT-HYBRIDS 53

the higher plants there goes a high degree of regenera-

tive power, a great contrast to the very limited capacity

for regeneration shown by the highly organized animals

where new individuals can only arise through sexual

reproduction. This great power of regeneration in

plants is accompanied by much less specialized cells and

a very imperfectly marked individuality of the organ-

ism as a whole. Any seed plant may be regarded as a

colony of individuals since the parts are repeated in-

definitely and can be made to regenerate the whole plant.

The power of regeneration shown by almost any part of

the plant, even a single cell in some cases, renders any

theory of a special germ plasm out of the question in the

case of plants, however plausible such a theory may ap-

pear when applied to animals.

It is not then so very extraordinary that this regenera-

tion of the plant from somatic cells should be carried so

far as to involve cell fusions such as Winkler believes

preceded the formation of his Solanum darwinianum.

Even if this should not be proved, his experiments show

beyond question the existence of graft-hybrids of a sort

quite inconceivable in any animals except very low types,

such as corals where it is by no means impossible that

similar graft-hybrids might be developed.

It is this positive demonstration of the reality of

‘‘vegetative’’ or ‘‘somatic’’ hybrids which gives the ex-

periments of Winkler their greatest value, and it is to

be hoped that they will serve as a stimulus to other work

in the same direction which may well have a great infiu-

ence upon the drift of biological speculations dealing

with the laws of heredity.

A DOUBLE HEN’S EG@

DR. J. THOMAS PATTERSON,

UNIVERSITY OF TEXAS

Dovuste hens’ eggs have always attracted much at-

tention and the literature covering the records and de-

scriptions of the various kinds has become extensive. In

a comparatively recent paper published in this journal,

Parker? has reviewed the main contributions to the sub-

ject and from a consideration of these, together with his

own observations on five double eggs, has been led to the

conclusion that at least two factors are involved in the

production of such eggs. According to him, double-yolk

eggs are produced when there is a simultaneous dis-

charge of two yolks from the ovary, whether these are

derived from a single follicle or from two separate fol-

licles ; while inclosed eggs may be the product of a normal

ovary and probably are produced through the abnormal

action of the oviduct, ‘‘in that a yolk normally supplied

by the ovary may be abnormally covered, retained and

inclosed in another egg.’? Parker therefore classifies the

factors concerned in the formation of double eggs as

ovarian and oviducal. Three types of double eggs result

from the action of these two factors: (1) those in which

the yolks have been derived from an abnormal ovary but

have traversed a normal oviduct, (2) those produced by

an ovary and an oviduct both of which have functioned

abnormally, (3) and those in which the yolks have come

from a normal ovary but have passed through an abnor-

mal oviduct.

The egg described in the following pages clearly be-

longs to the third type, and since it possesses certain

‘Contributions from the Zodlogical Laboratory of the University of

Texas, No. 107.

+‘ Double Hens’ Eggs,’’ by G. H. Parker, AMERICAN NATURALIST, Vol.

XL, 1906.

54

N’ S EGG

1

4

ae > 6

s

DOUBLE

A

No. 529]

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56 THE AMERICAN NATURALIST [ Vou. XLV

peculiarities that have not appeared in any previous ac-

count, seems to be worthy of record. It should be kept

in mind, however, that the value of such descriptions does

not come from the morphological features revealed, no

matter how bizarre these may be, but from the fact that

considerable light is often thereby shed on the complex

physiology of the reproductive organs, and it is with

this idea in mind that the following record is made.

The egg in question, which was kindly handed to me

by Mr. S. L. Pinckney, Austin, Texas, was laid March 28,

1910. It was stated that several double eggs had been

received from the flock from which this egg came, but

whether they were all laid by the same hen could not be

ascertained. The egg was large, measuring 85 mm. in

its long axis and 62 mm. in the short axis, and was

slightly smaller at one end than at the other, so that we

may speak of the blunt and pointed ends. It was prac-

tically a soft-shelled egg, in that the amount of lime de-

posited on the shell-membrane was very small, and for

the most part was collected into little nodules scattered

about over the surface (Figs. 1 and 2). A microscopical

examination of the shell-membrane did not reveal any-

thing unusual, for it consisted of the two characteristic

layers, a thick outer and a thinner inner; but on cutting

it open I was surprised to find another shell-membrane

lying almost directly beneath it (Fig. 2). The two mem-

branes were separated by the very thinnest layer of

watery albumen. This second or inner membrane was in

every way normal, and perfectly white, but was entirely

void of lime deposits, reminding one very much in its gen-

eral appearance of the membranes on eggs which have

just reached the isthmus.

The contents of the inner shell-membrane consisted of

much albumen in which were imbedded a hard-shelled

egg anda yolk (Fig. 3). Upon examination the inclosed

egg was found to be perfectly normal in every respect,

and its yolk contained a healthy blastoderm. The in-

closed yolk, although normal in structure, was much dis-

No. 529] A DOUBLE HEN’S EGG 57

torted, owing to the pressure exerted upon it by the ap-

proximation of the hard-shelled egg. The albumen

closely adhered both to the egg and to the yolk, but much

of it was of a liquid nature, as was indicated by the ease

= with which it flowed out of the cut first made in the inner

membrane.

The accompanying diagram will make clear the rela-

tion of the various parts of this interesting monstrosity

(Fig. 4). The inclosed egg lies toward the pointed end

4. Diagram of a median section of the egg. i.s.m., inner shell-mem-

brane, the two lines representing its two layers; 0.s.m., outer shell-membrane;

8, Shell of the inclosed egg; y, yolk of the inclosed egg; y’, yolk of the inclosing

egg. Natural size.

of the inclosing egg, and its long axis meets the corre-

sponding one of the double egg at an oblique angle. On

account of this inclination of the inclosed egg its pointed

end lies nearer to the blunt than to the pointed end of the

inclosing egg. The inclosed yolk occupies the blunt end

of the inclosing egg and is considerably distorted by

pressure. The chalaze are but poorly developed, but

the axis formed by a line passing through their points

of attachment to the vitelline membrane approximately

coincides with the long axis of the inclosing egg, showing

that the yolk has maintained its original orientation.

58 THE AMERICAN NATURALIST [ Vor. XLV

As I have pointed out above, the most interesting ques-

tion regarding this egg pertains to the physiology of its

formation. Parker states that two hypotheses have been

advanced to explain how inclosed double eggs are formed.

According to one of these, which was first advocated by

Panum,* the inclosed egg remains in the distal part of

the oviduct until overtaken by a second one, when both

are then surrounded by a common envelope; according to

the other a completely formed egg is carried by antiperi-

stalsis back up the oviduct, where it meets a second one,

and the two passing down become covered by a second

shell and are laid. It seems quite evident from the de-

scription of the egg just given that it is the product of

antiperistalsis, but the especial interest lies in the fact

that this process has taken place twice.

The first antiperistalsis took place immediately after

the hard-shelled egg was formed, and of course caused its

migration to the upper or proximal end of the oviduct

where it met the second egg. This meeting must have

taken place very close to the infundibulum, for otherwise

the yolk of the second egg would have possessed much

larger chalaze.

The second antiperistalsis occurred immediately after

the inner of the two shell-membranes had been laid down,

and must have succeeded in carrying the double egg up

the oviduct to a point where albumen is secreted, that is,

to a place slightly above the beginning point of the isth-

mus; for it is only on this assumption that we are able to

explain how a thin layer of albumen came to exist be-

tween the two shell-membranes. The small amount of

lime deposited on the outer of the two shell-membranes

indicates that the egg did not remain long in the uterus,

but must have been laid shortly after having entered that

organ.

In many respects this egg conforms to the facts already

seen in the inclosed types of double eggs; thus the in-

* Untersuchungen über die Entstehung der Missbildungen zunächst in

den Eiern der Végel,’’ by P. L. Panum, Berlin, 1860.

No. 529] A DOUBLE HEN’S EGG 59

closed egg lies near the pointed end of the inclosing one,

and it was laid during the time of year when such eggs

most frequently appear, that is, in the winter or spring;

but it differed in one rather important respect. The

pointed end of the inclosed egg does not lie in the same

direction as that of the inclosing one. This unusual

position of the inclosed egg doubtless has been brought

about by crowding, and does not indicate necessarily that

it was at first incorrectly oriented.

Among the more important things so far revealed by

a study of inclosed double eggs is the light thrown on the

problem of the orientation of the egg in the oviduct, a

problem in which the writer has been deeply interested.

These eggs clearly demonstrate that when an egg has

once entered the oviduct its original orientation in that

organ is maintained during the formation of the enve-

lopes, no matter to what extent it may have been moved

up and down the reproductive passage. This fact

strongly supports the conclusion reached by the writer‘

in a recent contribution, in which it was pointed out that

the definite orientation of the egg in the reproductive

passage is not a matter of chance, but is something that

is handed on to the oviduct by the ovary, that is to say

that the ova in the ovary have a definite polarity which

is passed on to the oviduct through the mechanism of the

infundibulum.

*‘‘The Early Development of the Hen’s Egg, I., History of the Early

Cleavage and of the Accessory Cleavage,’’ by J. Thomas Patterson, Journal

of Morphology, Vol. 21, 1910.

NOTES AND LITERATURE

HEREDITY

One of the most important papers relating to heredity that

has appeared in recent months is that of Tower, dealing with

hybridization investigations with species of the genus Leptino-

tarsa. I shall not here attempt an extensive review of this

paper, but mention it rather as a means of calling attention to

its importance and suggesting that any one interested in theo-

retical discussions of heredity should not fail to read it. Tower

has done an immense amount of work with this genus. His re-

sults lead him to accept the factorial hypothesis as an explana-

tion of Mendelian phenomena but to discard wholly the de

Vriesian interpretation of these factors. The most important

contribution in this paper is the apparent fact that the environ-

ment at the time when eggs are fertilized may change very ma-

terially the nature of the hereditary factors. It is unfortunate

that the author does not give more details in connection with

this conclusion. The data he does give are mixed and contra-

dictory. There has possibly been an error in printing Tower’s

paper, but if not there was a serious error in its preparation, as

will be seen from the following. In experiment 409, which was

several times repeated, the results were exactly as if one of the

parents had been a heterozygote between the two species. F, con-

sisted of two types, one of which was identical with the female

parent and the other intermediate between the two. The one

like the female parent bred true to that type, while the other

behaved in all respects as a heterozygote. In experiment 410-

the same two species were utilized, but the temperature and

humidity conditions at the time the eggs were fertilized were

made quite different. This experiment, which was repeated

eleven times, gave in every case ordinary Mendelian phenomena.

In experiments 409/411, which was performed seven times,

one set of eggs from the same cross as above was produced

under conditions identical with those of experiment 409, and in

* Tower, Wm. L., ‘‘ The Determination of Dominance and the Modifica-

tion of Behavior in Alternative (Mendelian) Inheritance, by Conditions

Surrounding or Incident upon the Germ Cells at Fertilization,’’ Biol. Bull.,

XVIII, No. 6, May, 1910

60

No. 529] NOTES AND LITERATURE 61

each case gave identical results with those of 409; that is, F,

consisted of two types, one heterozygote, and the other homozy-

gote of the maternal type. Using the same individuals which

produced a set of eggs of this kind to secure another set of eggs

produced under the conditions of experiment 410, the results

in each of the seven experiments gave F, which behaved in all

respects as a homozygote of the maternal type. This fact is set

forth in considerable detail and Plate III illustrates it just as

here described. This result occurred in all cases whether the

set of eggs produced under the conditions of experiment 410

was produced before or after the set which gave the results of

experiment 409. Now the remarkable thing about this experi-

ment is this. While in experiment 410 the results in each of the

eleven cases gave ordinary Mendelian heterozygotes in F,, in

each of the seven cases of 409/411 the eggs produced under the

same conditions as 410 gave homozygotes of the maternal type.

Thus, the conditions of experiment 410 in eleven cases gave one

result, in seven other cases they gave an entirely different re-

sult, and the only difference in the conditions was that in

409/411 the female either had produced or was in the future

to produce a set of eggs under the conditions of experiment 409

(p. 295).

Thus, on page 294, in describing experiment 410, it is stated

that experiment 410 gave F, all heterozygote; on page 330 it is

stated that experiment 410 gave F, all homozygote of the ma-

ternal type; on page 295-6, in describing experiment 409/411,

it is stated that, under the conditions of experiment 410, this

experiment gave F, all homozygotes of the maternal type; and

on page 304 it is stated that experiment 409/411, when per-

formed under the conditions of 410, gave results identical with

those of 410. These statements are directly contradictory.

We must withhold judgment on this point of influencing the

hereditary factors at the time of fertilizations, until Mr. Tower

informs us which of these statements are correct.

In these exceptional cases, where the F, hybrid behaved as a

homozygote of one of the paternal races, the author does not

tell us whether the F, and later generations were each time pro-

duced under the conditions which produced the aberrant F,.

One would infer, however, that they were not, and that the

change which occurred in the fertilization of the eggs which

produced F, was permanent and not reversible. It is hoped

62 THE AMERICAN NATURALIST [Vou. XLV

that he will give us fuller data on this point in future papers

which are promised.

In several cases Tower mixed three species which interbred

freely and left them under natural conditions for several years.

A careful study of the progeny in each case showed that a new

type arose, consisting of a complex of the characters of the old

types, and that this new type rather rapidly replaced every

other type, although some of these other types were known to be

quite capable of existing under the conditions of the experi-

ment. This would indicate that in some way the new type had

a distinct advantage over the other types with which it com-

peted for food, or possibly the repeated crossing of the types

was in some way inimical to all the types except the one. Ex-

periments of this character show that hybridization may be an

important factor in the development of new varieties or pos-

sibly new species.

From the fact that when the same species are mixed together

in two places where the conditions are different, the resulting

type which finally wins out and becomes practically the sole

representative of the mixture, is different under different con-

ditions. Tower draws the conclusion that the conditions sur-

rounding the germ cells at the time of fertilization ‘‘ profoundly

- modify the behavior and the relationships of the characters en-

tering into the crosses.’ This conclusion seems hardly justified.

Of course it may be correct, but the well known fact that from

complex crosses of this kind a great many types may result

from what we know of the behavior of Mendelian characters

‘and that these types would naturally bear different rela-

tions to the environmental conditions offers apparently a

much simpler explanation of the reason for the survival of

the one type under one set of conditions and another type

under another set of conditions. It seems hardly necessary

to assume that the conditions existing at the time of the fertil-

ization of the egg determine the characters which were to result

from the fertilization to explain this particular phenomenon.

Subsequent investigation of these new types of mixed origin

showed that in all cases they occasionally produced individuals

different from the general population but which in all cases ex-

hibited characters which were present in the original parents

of the complex mixture. Tower repeatedly compares this phe-

nomenon to the phenomena which de Vries observed in (no-

No. 529] NOTES AND LITERATURE 63

thera lamarckiana, and suggests that the mutations which de

Vries observed are probably due to previous hybridization.

This is a very interesting suggestion, but the writer is

inclined to believe that the phenomena observed by de Vries

were due to a different cause. It is definitely proved that

in some of de Vries’s mutants the chromosome numbers are dif-

ferent from those of the parent form. Cytological investiga-

tions have also shown that in the reduction division in these

(nothera mutants there are frequent irregularities in the dis-

tribution of chromosomes. It seems probable that de Vries’s

mutations are not the result of previous hybridizations but

rather are due to irregular behavior of chromosomes in the re-

duction division. If this is true then the phenomena observed

by de Vries would be due to a different cause from that which

presumably produced the results which Tower observed. In

the case of Tower’s results we can explain the facts by the as-

sumption of simple Mendelian segregation. In de Vries’s work

there is evidence that the phenomena are due to a different

cause.

It is gratifying that Tower takes a very broad view of the fac-

torial hypothesis of Mendelian phenomena. On page 323 he

remarks:

This factorial point of view is in no wise, of necessity, to be tied to

or confounded with such speculations as the id-determinant-biophore

fabrie of Weismann, nor with the pangene complex of de Vries, which

have no foundation in fact. :

This is the view which the writer has held for years and has fre-

quently set forth in these pages. I have also frequently pointed

out that we do not yet have sufficient knowledge of the phys-

iological processes of living matter to permit us at the present

time to formulate an adequate theory of the phenomena ob-

served in hybrids. I think we can, however, point out the gen-

eral nature of the causes underlying these phenomena, as I

have attempted to do in my theory of Mendelian phenomena.*®

In speaking of the difference in germ cells with respect to given

characters, he has the following to say:

What this difference in the gametes is we do not know, but observed

behaviors are interpreted as being, most probably, due to the mechan-

ical separation into different germ-cells of whatever it is that produces

the contrasting attributes—segregation during gametogenesis.

* American Breeders’ Magazine, Vol. I, No. 2.

64 THE AMERICAN NATURALIST [ Vou. XLV

He further remarks on page 328:

At present in biology we have no business with ultimate conceptions,

and the two thus far attempted of germinal composition—the “ par-

ticulate conception ” and the “crystalline entity” are both equally

dismal failures and equally useless as working hypotheses.

The statement on page 335, that characters which Mendelize

are in the main unimportant attributes of the organism and

only rarely are of importance in the struggle for existence,

is a little bit strong. Apparently it would have been better to

state that those characters which have been shown to Mendelize

are of this nature. Unfortunately, most of the work of the

Mendelians has been done with these superficial, easily observed

characters. I see no reason why any character whatever might

not, from the failure of some chromosome to perform a usual

function, give a variation which would behave in Mendelian

fashion if the resulting type were capable of propagating and

crossing with the parent type.

Tower’s paper will undoubtedly have an important influence

on biological thought, as it deserves to have.

W. J. SPILLMAN.

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The American Naturalist

A Monthly i established in 1867, Devoted to the Advancement of

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CONTENTS OF THE JULY NUMBER

A SS of the “Species Plantarum” of Linnaeus

r the Starting Point of the oe

of percha Professor W. G. Far

Notes on Some Beaufort Fishes. E. W. vrei

On the Effect of — Conditions = ae Reproduc-

aphnia. Dr. J. F. McCLEN

Are Fluctuations aay Dr. HARRY ne ‘Love.

P Professor EDWARD Fr East.

~~. ap ~ and Se ap seacivayeighy The Age

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neg Sfodifeaton of the Mendelian s, Pro-

The Bubonic Peas "Proessor

H E Was: os ai P Plants, WILLIAM L. Bray,

CONTENTS OF THE AUGUST NUMBER

Chromosomes and Heredity. Professor T. H. MORGAN.

Spiegler’s “White Melanin” as Related to Dominant or

Recessive White. Dr. Ross AIKEN GORTNER.

Shorter Articles and Correspondence: A Pickwickian

Contribution to Our Knowledge of Wasps: Professor

KARL PEARSON.

Notes and Literature: Heredity, Dr. W. J. SPILLMAN.

CONTENTS OF THE SEPTEMBER NUMBER

Nuclear swig of Sexu: eae in the

Alge. Dr. BRADLE

Y Moor: D

TE Phenomena of Sexual ceai in Fungi,

R R. A. HARPER.

The Pose A the Sauropodous Dinosaurs. Der. W. D.

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Shorter Articles and Discussion: Evolution without Iso-

lation, Dr. oe T. GULICK. Retroactive Selection,

Casper REDFIELD. The Logic of Chance in

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Notes and Literature: Animal Structure and Habi

Professor G. H. Parker. Plant Physiology, C. Ñ

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CONTENTS OF THE OCTOBER NUMBER

hrant = Urosalpinx. Dr. HERBERT EUGENE

AAE D ~ Sexual Reproduction in Gym-

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Shorter Articles and Discussion : ‘mae Dr. Max

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Notes and Lite

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: Notes on Ichthyology, Presiden’

The Mammals of ere

CONTENTS OF THE NOVEMBER NUMBER

gassed of Skin Pigmentation in gee GERTRUDE C,

VENPORT and CHARLES B, DAVENPORT.

The yes Sense of the pany mesg: Bees distinguish

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Shorter Articles ane sa sya Anta oF the

Product apea Method o oef

cient of Correla’ ¥ Dr, J: j sa HARRIS.

Notes and Literature: Schlosser on Fayûm Mammals,

Dr. W. D. MATTHEW. Pei rere acgeen Genus Grayia:

Professor T. D. A. Coc

CONTENTS OF THE DECEMBER NUMBER

Heredity of cosmid Pi “een in Man. GERTRUDE c.

DAVENPORT RLES B. DAVENPORT.

oe and Larva a Amie Jeffersonianum. Pro-

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The RA ena of Sizes a Shapes in Plants. Professor

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THE

AMERICAN NATURALIST

VoL. XLV February, 1911 No. 530

THE APPLICATION OF THE CONCEPTION OF

PURE LINES TO SEX-LIMITED INHERI-

TANCE AND TO SEXUAL DIMORPHISM!

PROFESSOR T. H. MORGAN

COLUMBIA UNIVERSITY

In the same sense in which our ideas concerning

variation and heredity have been entirely revolutionized

since 1891, so has a similar change taken place in regard

to our theories of sex determination. Sex is now treated

by the same methods that are used for Mendelian char-

acters in general. From this point of view I propose to

consider to-day three questions, intimately associated.

First, the treatment of sex as a Mendelian character;

second, the relation between sex and the inheritance of

secondary sexual characters; third, the bearing of the

recently discovered cases of ‘‘sex-limited-inheritance’’

on the problem of the transmission of characters in

general.

Most modern theorists are in agreement that the

heredity of sex can be best understood when one sex is

regarded as a pure line, or homozygous, and the other

sex is treated as a phenotype, i. e., as heterozygous.

The experimental evidence has made it plain that in

some animals and plants it is the female that is hetero-

zygous, and in other animals and plants it is the male

that is heterozygous. Hence have arisen through the

necessities of the situation the two following classes of

formule :

‘From a symposium on ‘‘The Study of Pure Lines of Genotypes,’’

before the American Society of Naturalists, December 29, 19-4,

65

66 THE AMERICAN NATURALIST [Vou. XLV

Gametes

od Female F 8

gő Male OOS

g

female male

99 Female g ?

Q¢ Male oOo S.

2

female male

In certain groups of animals, as in Abraxas amongst

insects, and in poultry amongst birds, the first scheme is

essential to an interpretation of the facts obtained by

experiment. In other groups, as in Drosophila amongst

insects, and in man amongst the vertebrates, the second

scheme accounts for the experimental results.

These methods of formulation are open to two serious

objections. As the tables show, the combination of 2¢

stands for the female in one case, and for the male in the

other. In order to avoid this apparent contradiction it

is assumed that in some groups femaleness dominates

maleness, and in other groups maleness dominates fe-

maleness, which seems to me paradoxical at least.

It will be observed also that in the first of these

schemes the male carries none of the sexual characters

of the female, and in the second scheme the female car-

ries none of those of the male; both of which assump-

tions do not seem to me to be completely in accord with

fact. Cytologists represent these same two schemes in

a different way. They represent in the one case the

female character by X; and the male by the absence of

X. Thus:

Gametes

XO Female x

OO Male o oO

ao CO

female male

This representation covers the first class of cases

where the female is heterozygous. For the second class,

where the female is homozygous, the following scheme is

No. 530] CONCEPTION OF PURE LINES 67

used, in which the female is represented by two X’s and

the male by one X:

Gametes

XX Female

XO Male x (0)

AX 30

female male

The XO—OO scheme applies, as before, to the case of

Abraxas and to poultry, and the XX—XO scheme to the

other class of cases. The latter expresses also exactly

what takes place in the chromosomes of those groups

where two classes of sperm exist (in relation to the X

element), as has been demonstrated by Stevens and by

Wilson.

In both of these two latter schemes the production of

the female is ascribed to the presence of the chr e

X, but in the first formula one X makes the female and

its absence stands for the male, while on the second

formulation two X’s make the female, while one makes

the male. In one case XO is female and in the other XO

is male. Again we meet with the same paradox as in

the first two formulations.

The chief drawback to these formule is, in my opin-

ion, the absence of any character to stand for maleness.

Absence of femaleness does not appeal to me as a suffi-

cient explanation of the development of a male; for the

male is certainly not a female minus the female char-

acters.

Nevertheless, despite these objections I am inclined

to think that these two methods of formulation indicate

the direction in which we must look for an explanati

of the experimental evidence, and that they may be still

utilized provided we can so modify them that their in-

consistences can be made to disappear.

It seems to me that if we are to succeed in bringing

Sex into line with Mendelian methods we must be pre-

pared to grant that there are representative genes for

the male condition and others for the female; and we

must so shape our formule that the female carries the

68 THE AMERICAN NATURALIST [ Von. XLV

genes for the male and the male carries those for the

female. In fact, I am inclined to think that the evidence

forces us to accept Darwin’s original view, that in each

sex the elements of the other sex are present; a view that

has been largely given up by modern theorists (except

by Strasburger). I think that we must accept this in-

terpretation for several reasons. Every zoologist is

familiar with cases in which the same individual may at

first function as a male and later as a female. More re-

markable still is the case of the Nematodes in which in

some species the female has come to produce both eggs

and sperm as shown by Maupas and more recently by

Potts, while in another closely related species it is prob-

ably the male, according to Maupas and Zur Strassen,

that has come to produce eggs as well as sperm. There

is further the class of cases where the female develops

the male secondary characters and the male those of the

female. This class of cases I shall discuss later, for the

value of this evidence will turn on whether these second-

ary sexual characters are represented by independent

genes, or are expressions of the presence of one or the

other sexual condition; or due to a combination of these

two possibilities.

By means of the following formule we can meet the

requirements that the situation seems to me to demand.

If we admit that in the first class one of the genes has

become larger than the other female genes, and if we

admit that in the second class one of the female genes

has become smaller than its sister genes we can account

for the results as the following formule show:

Gametes

Fmfm Female

fmfm Male fm fm

Ffmm ffmm

female \ male

FmFm Female Fm X Fm

Fmfm Male Fm \ fm

PASSES, geome

FFmm Ffmm

No. 530] CONCEPTION OF PURE LINES 69

It should be carefully observed that in this scheme the

female genes, F or f pair when they meet (allelomorphs) ;

likewise the male genes‘ pair only with male genes. In

fact, both genes are carried by all of the gametes. Sex-

ual dimorphism may appear either because one female

gene has become stronger than the others, or, because

one has become weaker. On the first view we have

the case where the female is heterozygous in its female

genes; in the latter case it is the male that is heterozy-

gous in its female genes. If in this latter case we as-

sume that the weakened female gene is contained in the

so-called Y-chromosome we can then understand how it

is that we have a degraded series of this chromosome

leading in some forms to its final extinction, for even its

disappearance leaves the formule unaffected. On the

same grounds we may anticipate that in those species in

which the X elements are alike in the male, one X in

the female may be found larger than its partner, al-

though visible size differences in the chromosomes are

not essential to the scheme, since these chromosomes

undoubtedly contain many other factors than those of

sex whose presence might obscure size relations even

when such exist in the sex genes.

These formule appear more complicated than those

previously given, but in reality they are not so. It is

the presence of m in all of the gametes that gives the

appearance of complication. If this is omitted, as in the

formula given below, the formule are no more complex

than those given earlier.

Gametes

Ff Female

ff Male f f

Ff ff

FF Female F F

Ff Male F £

FF Fe

The formule might be further simplified, if it seemed

desirable to do so, by simply indicating the determining

factor in each case as shown below; thus:

70 THE AMERICAN NATURALIST [ Vou. XLV

Gametes

FO Female

OO Male O O

FO (010)

OO Femalə (0) O

Of Male O f

o0 Of

But this last simplification is misleading, if the thesis

that I shall here maintain in connection with sex-limited

inheritance is correct; because the F’s and the f’s

omitted in the last case are supposed to be carried in

definite bodies, the chromosomes, which also carry other

factors than sex factors, and it is essential to indicate

their presence in some way in order that these other fac-

tors may have some means of transportation.

In a recent paper on sex determination in phylloxerans

and aphids (1909) I discussed at some length different

theories of sex determination, and adopted provisionally

the view that the outcome is determined by a quantita-

tive factor. The present hypothesis is little more than a

further development of this same view,” but I hope in a

form more in accord with the Mendelian treatment of

the problem. Sex is still represented as the result of a

quantitative factor F (or f), but its relation to the male

factor is now expressed, for maleness is not assumed, as

before, to be no femaleness or less femaleness. Here, as

there, more of a particular factor turns the scale towards

femaleness in the first class of cases, and less of the fe-

male factor allows the scale to turn in the opposite direc-

tion in the second class of cases.*

2 In 1903 I suggested that in the case of the bee a quantitative factor

determines sex, viz., the chromatin; two nuclei producing a female and one

a male, Wilson (1905) has identified the quantitative factor with a special

chromosome and this interpretation of the quantitative factor is here fol-

lowed. On Wilson’s view the male condition is represented by the absence

of the X-chromosome in some cases, and by the presence of only one X-

chromosome in the others, (see ante); but on my view the determination of

sex is regulated by this quantitative factor in relation to another factor,

the male determining element.

*It should be pointed out that these formule are in no way related to

a suggestion that I made in 1907 in regard to dominance and recessiveness

No. 530] CONCEPTION OF PURE LINES 71

These formule have certain advantages over those

now in vogue, first, because the male gene is not ignored

as a factor in sex determination; second, that its pres-

ence, both in males and females, explains how under cer-

tain conditions the male or the female may assume some

of the characters of the opposite sex; third, that the

paradox of the female being the heterozygous form in

one class and the male in the other class is, in part at

least, resolved; fourth, that the ease with which species

pass from the hermaphrodite condition to that of sexual

dimorphism and the reverse is understandable; fifth,

that the production of males by parthenogenetic females

can be accounted for by the loss of one of the female

genes in the polar body; and lastly, we see how there

may be two kinds of eggs, as in Dinophilus apatris, both

of which can be fertilized; for, in such cases the sperma-

tozoa should be all alike.

I do not wish to urge this view too positively, for I am

acutely aware that we are only at the beginning of our

understanding of the problem of sex determination, but

I believe that the difficulties of the current hypotheses

must be clearly understood and met if possible.*

THE INHERITANCE OF SECONDARY SEXUAL CHARACTERS

From the point of view reached in the preceding dis-

cussion let us now examine the problem of the inherit-

ance of secondary sexual characters.

Males are distinguished from females not only by the

presence of sperm in place of eggs, but by the presence

in general. That view I have entirely abandoned. In the present hypoth-

esis the relation of the determining elements is stated in the same form as

in other Mendelian formule, with the possible exception that here one gene

is represented as larger or smaller than its allelomorphs, and the scale is

turned by the mass relation between these female genes and those of the

male,

*I have not discussed here the possibility of selective fertilization,

because if we can explain the facts without this problematical assumption

we simplify the problem greatly. Moreover, the evidence brought forward

by Payne, Brown and myself, while admittedly insufficient, stands definitely

opposed to the view of selective fertilization.

72 THE AMERICAN NATURALIST [ Von. XLV

of different kinds of ducts, glands, copulatory organs, or

other accessory sexual apparatus; and also by structures

not essential to reproduction. These last we call the

secondary sexual characters.

It has long been known that in the embryonic develop-

ment of the vertebrates some of the accessory organs of

the male appear in the female, and conversely some of

the accessory organs of the female in the male. This

evidence seems to me to point with no uncertain mean-

ing to the conclusion that each sex carries the genes of

the other. It is however the secondary sexual characters

rather than these accessory organs of which I wish to

speak now; for, these often appear to be present in one sex

only. Are these characters represented in all eggs and

sperm or are they by-products of the sexual condition of

the animal? Fortunately there is a good deal of experi-

mental evidence that bears on this question, but it is also

true that the evidence teaches that the matter must be

handled with care, and if I seem to speak dogmatically

it is for lack of time rather than for want of caution.

It has been shown by Meisenheimer that removal of

the gonads of the caterpillar of Ocneria dispar fails to

produce any effect, or very little, on the secondary sex-

ual characters of the moth. It would seem, therefore,

that these characters are represented in the germ cells in

the same way as are other characters, and are not depend-

ent for their development on the presence of the gonads.

Some mechanism must exist by means of which the genes

of these organs are distributed so that two kinds of in-

dividuals are produced. It has been suggested by Castle

that the secondary sexual characters may be carried by

the Y-element in the formule XX — female, XY — male,

but this hypothesis fails to explain the results when the

Y-element is absent, as E. B. Wilson has pointed out. It

also fails to explain how the male secondary sexual or-

gans can appear in the female after castration.

On the sex formule that I have suggested it is pos-

sible to account for the results, if the genes for these

No. 530] CONCEPTION OF PURE LINES 73

characters are carried by all cells alike; possibly they go

along with the male-group, but this is not essential.

Whether they develop, or not, will depend on the pres-

ence of other genes in the cells. Thus when the Fmfm

group is present they will be suppressed, or when, as on

the other formule, the FmF'm group is present. We can

understand on this view why in the insects the male sec-

ondary sexual organs do not develop in the female after

removal of the ovaries, because in this group it is not

material derived from this source, but from materials

produced in the cells themselves, that bring about the

suppression.

It has been demonstrated by Geoffroy Smith that

when the young males of the spider crab, Inarchus mau-

‘retanicus, are infested by Sacculina the secondary sex-

ual characters of the female develop. It appears that

the parasite produces some substance that inhibits the

activity of the male-producing group in each cell, or

counteracts some materials produced there, so that the

female characters now find the situation favorable for

their development. When the young female crab is in-

fected by Sacculina she does not develop the male sec-

ondary characters, which is in harmony with the view

just stated for the manner of action of the parasite.

In birds and in mammals it has long been recognized

that some substance is produced in the ovary that in-

hibits the development in the female of the male second-

ary sexual characters, for, after removal of the ovaries

the male characters may to some extent develop. It

seems fairly clear that here the female group in each

cell fails to entirely suppress the male characters; the

inhibiting effect from this source must be reinforced

from something produced in the ovary. Whether after

castration of the male the secondary sexual characters

of the female develop is not so clear, since some at least

of the characters that characterize the castrated male

may be juvenile. But on my view the possibility exists

for the castrated male to produce the secondary sexual

74 THE AMERICAN NATURALIST [ Vou. XLV

characters of the female, if their development is in part

suppressed by substances made in the testis.

The view here presented also allows us to explain how

the secondary sexual characters of the male are trans-

mitted through the female, as they may be so transmitted.

THE INHERITANCE OF SEX-LIMITED CHARACTERS

In recent years a new class of facts has been discov-

ered that promises to throw a flood of light not only on

the sex-determination problem, but also on the problem

of inheritance in general. I refer to the cases of sex-

limited inheritance.

We mean by sex-limited inheritance that in certain

combinations a particular character appears in one sex

only. An example will make this clear. In one of my

cultures of the red-eyed fly, Drosophila, a white-eyed

male appeared. Bred to red-eyed females, all of the off-

spring, male and female alike, had red eyes. These

inbred produced red-eyed males and females, and white-

eyed males. In other words the white-eyed mutant

transmitted his character to half of his grandsons, but

to none of his granddaughters.

Yet this white-eyed condition is not incompatible with

femaleness; for, it can be artificially carried over to the

female by making a suitable cross. If, for instance, a

white-eyed male is crossed with a heterozygous red fe-

male, there will be produced red-eyed males and females

and white-eyed males and females.

There are certain combinations of sex-limited char-

acters that give results outwardly similar to sexual

dimorphism. If a black langshan cock is crossed to a

dominique hen, all of the sons are barred and all of the

daughters are black. If a white-eyed Drosophila female

is crossed with a red male all of the sons will have white

eyes, and all of the daughters will have red eyes. I have

another strain of these flies with small wings and still

another strain with truncated wings. If a female of the

former is crossed with a male of the latter strain all of

No. 530] CONCEPTION OF PURE LINES 16

the daughters will have long wings and all of the sons

will have small wings, like their mother.

These cases conform to Mendel’s principle of segrega-

tion. Were there time I could show by an analysis of the

problem why these sex-limited characters behave in in-

heritance in a different way from secondary sexual

characters, although the results in both cases may be

accounted for on the assumption that there are genes in

the cells for both kinds of characters. In a word, this

difference exists because one of the factors for the sex-

limited characters in question is absent from one of the

female determining chromosomes, while the genes for the

secondary sexual characters of the male are contained

in other chromosomes, possibly in those that contain the

male determinants.

This interpretation of the relation between the X-

chromosomes and sex-limited characters makes it now

possible to demonstrate a point of great theoretical im-

portance. I invite your serious attention for a few

moments longer to this question. Three other characters

have appeared in my cultures that are sex-limited; one

of these only I may now speak of. A male with wings

half the normal length suddenly appeared. He trans-

mitted his short wings to some of his grandsons, but to

none of his granddaughters. I tried to see if the other

sex-limited character, white eyes, could be combined in

the same individual with short wings. As the next dia-

gram shows a red-eyed short-winged male was bred to a

white-eyed female with normal wings. All of the off-

spring had long wings; the female had red eyes and the

males white eyes. These were inbred and produced

white and red-eyed males and females with long wings,

red-eyed males with short wings, and white-eyed males

with short wings. In the last case the transfer had been

made. The reciprocal cross also given in the diagram is

equally instructive.

76 THE AMERICAN NATURALIST [ Vou. XLV

LWF — LWF Long-winged, white 9

SRF O Short-winged, red g

LWFSRF — LWF

LWF SRF SWF LEF = 9 Gametes

F— oO g Gametes

LWFLWF Long-winged Ọ white eyes

SRFLWF Long-winged Ọ red eyes

SWFLWF Long-winged ? white eyes

LRFLWF

n

SRF Short-winged ¢ red eyes

SWF Short-winged & white eyes

LRF Long-winged ¢ red eyes

LRF LRF Long-winged, red 9

SWF O Short-winged, white ¢

LRFSWF — LRFO

LEF SWF LWF 8RF 9° Gametes

LRF O g Gametes

LRFLRF Long-winged ? red eyes

LRF ong-winge red ey

SWF Short-winged 4 white eyes

LWF Long-winged ¢ white eyes

SRF Short-winged g red eyes

In both cases the combination is possible because in

the female of the hybrid (F,) a shifting of the gene for

long and that for short wing (both carried by the X-

chromosome) takes place. This interchange is possible

during the synezesis of the two X-chromosomes. On the

other hand the male contains only one X-chromosome

which has no mate, hence the gene for long wings in the

hybrid (F,) can not leave that chromosome to pass into

the male-producing group. If it could do so short-winged

females would also appear, but as I have shown they are

not present in the second generation.

Interpreted in terms of chromosomes these results can

have, in my opinion, but one meaning. During union of

homologous chromosomes (during synezesis, perhaps)

homologous genes pair and later separate to move to op-

No. 530] CONCEPTION OF PURE LINES 77

posite sides (or enter the chr sometimes one

way and sometimes the other). All the genes contained

in the X-chromosomes can thus shift in the female be-

cause in this group two X’s are present. Sex-limited

inheritance is only possible where similar conditions

exist (either in the male or in the female) and since in

man color blindness follows the same scheme as does

white eyes in my flies, we have an experimental proof that

in the male of homo sapiens there is only one X-chromo-

some, and this, in fact, Guyer has just shown to be the

case from cytological evidence. But by parity of rea-

soning it is the female in Gallus bankiva that should have

_ only one X present, but Guyer is persuaded that here too

(at least in the race of fowls he studied) the male has

only one X-chr . There is then in this case a

contradiction between the experimental evidence and that

furnished by cytology and it remains to see which is

correct.

Bateson has shown that some of these cases of sex- -

limited inheritance can be explained on the grounds that

there is a repulsion between the female-determining fac-

tor and that character that is sex-limited. The view that

I maintain does not involve the idea of a repulsion be-

tween unlike elements, not allelomorphic. Spillman’s

hypothesis also involves this idea of repulsion between

unlike elements. On my view, on the contrary, an at-

tempt is made to show how the results may be due to a

connection existing between certain material bodies in

the egg; a connection that is consistently carried through

successive generations, and subject only to the ordinary

interchange of genes between homologous chromosomes

(when a pair of chromosomes is present).°

For several years it has seemed to me that the chromo-

some hypothesis, so called, could not be utilized to ex-

plain the Mendelian results in the form presented by

ë The hypothesis advanced here to explain sex-limited inheritance applies

also to Abraxas if the latter follows the Fmfm scheme and if in the egg

there is no interchange between the F-bearing and the f-bearing chromo-

somes,

78 THE AMERICAN NATURALIST [Vou. XLV

Sutton, because, if it were true, there could be no more

Mendelian pairs in a given species than the number of

chromosomes present in that species. Even if this ob-

jection could be avoided® the more serious objection still

remained, namely, that with a small number of chromo-

somes present many characters should Mendelize to-

gether, but very few cases of this sort are known. De

Vries was the first, I believe, to point out that this objec-

tion could be met if the genes are contained in smaller

bodies that can pass between homologous pairs of chro-

mosomes; and Boveri has admitted this idea as compat-

ible with his conception of the individuality of the

chromosomes, In the case of the inheritance of two sex-

limited characters in the same animal we have an experi-

mental verification of this hypothesis.

°Spillman’s suggestion that the difficulty exists only when it can be

shown that more dominant characters can occur in the same individual than

the number of chromosomes seems to me only to push back the difficulty.

PURE LINES IN THE STUDY OF GENETICS IN

LOWER ORGANISMS!

PROFESSOR H. S. JENNINGS

THe JoHns HOPKINS UNIVERSITY

Art the meeting of this society a year ago I asked in a

paper read,? whether the pure line idea did not deserve

agitating a little before this society, and I tried to agitate

it. This was because I saw that for practical purposes

of future work it would be necessary to make up my mind

as to the importance of this idea, and it seemed that other

members of the society might be in the same situation and

that we might help one another. My method of agitation

was to give the apparent relations of the results of work

along this line up to that time, to one of the burning

problems in our field—the problem of selection. In the

few minutes that each of us have here the purpose of

agitation can be served and general results brought

sharply into view only by naked and dogmatic statements,

such as one would never use under other conditions.

Such naked and dogmatic presentation has serious dis-

advantages—felt most decidedly by the author when his

critics hold the mirror up to nature. I have therefore at

times regretted giving forth this paper. But if it has in

any way acted as an irritant to arouse the discussion fore-

shadowed in our present program, I shall feel that its

good results outweigh its painful ones, and that it was

worth while after all. We are apparently to have >

brought before us a part of that ‘‘thorough try out’’ that

I asked for, and from a study of our program I think I

can see that it is not all to be a pean of praise for the pure

line work. Such illumination and such interest as comes

m a symposium on ‘‘The Study of Pure Lines or Genotypes,’’ be-

* Fro;

fore the Ameriean Society of Naturalists, December 29, 1910.

* This JouRNAL, March, 1910.

79

80 THE AMERIGAN NATURALIST [ Vou. XLV

from having both sides presented I believe that we have

before us.

What I wish to attempt is to give some concrete illus-

trations of the answer to the question discussed by Dr.

Webber— What are genotypes? I note that some of the

titles on our program speak of the genotype hypothesis,

the pure line theory. What I wish to emphasize is that

these things, whatever we call them, are concrete realities

—realities as solid as the diverse existence of dogs, cats

and horses. I find in many biologists not working in

genetics an incorrigible bent for seeking under such a

term as genotype something deeply hypothetical or meta-

physical, and for characterizing it therefore boldly as

purely imaginative. This is merely because such

workers have not the things themselves before them.

The genotype is merely a race or strain differing heredi-

tarily in some manner from other races. Neither the

idea nor the fact is a new one, and we should perhaps do

better to discuss merely the importance of distinguishing

in our work the diverse existing strains—rather than to

introduce an unfamiliar term for a familiar thing. But

investigation has shown the existence of these strains to

play a part of such hitherto unsuspected importance that

it has seemed worth while to introduce a more precise

term, which shall emphasize their importance for work in

genetics. In work with a certain lower organism—

Paramecium—t have found the existence of these diverse

strains or genotypes to be the guiding fact, not only for

work in genetics, but for all exact work in comparative

physiology. I wish to show how this is true.

We must then distinguish clearly these concrete

realities called genotypes from any theories that have

been built up in connection with them; from any generali-

zations based on their study up to this time. The exist-

ence and importance of genotypes are not bound up with

any particular theory regarding selection or any other

single point. In lower organisms, at least, genotypes OT

pure lines are merely the name for certain actual exist-

ences that you have before you; for facts that strike you

No. 530] PURE LINES IN STUDY OF GENETICS 81

in the face. We have, side by side in the laboratory, a lot

of diverse sets of our organisms, each set derived origin-

ally from one individual, and each differing characteris-

tically but minutely from the others—the differences per-

sisting from generation to generation. The behavior and

properties of these things are of course a matter for

further study. Can selection change them? Can envi-

ronmental action permanently modify them? These are

matters quite distinct from the existence of the genotypes.

To get a clear grasp of the matter, I believe that those

not working with lower organisms will find it worth while

to try to realize the condition which the investigator in

this field has before him. A comparison may help. In

lower organisms the genotype is actually isolated, each in

a multitude of examples, which live along without admix-

ture, visibly different from all others, for many genera-

tions, before again plunging into the melting pot of cross-

breeding. In higher organisms we should have the same

thing if every rabbit, every dog, every human being,

multiplied by repeated division into two like itself, till

there were whole counties inhabited by persons that were

replicas of our absent president; cities made up of copies

of our secretary, and states composed of duplications of

the janitor I saw outside. Every human being, as it now

stands, represents a different genotype (save perhaps in

the case of identical twins), and these genotypes become

inextricably interwoven at every generation. It is there-

fore easy to see how the genotype idea might appeal to

workers among higher organisms as a mere hypothesis.

What then are these visible, tangible, isolated geno-

types (or races, or strains) of lower organisms, and how

are they distinguished? Taking Paramecium as a type:

1. Some of them differ in size—the size of each remain-

ing closely constant, under given conditions, for hundreds

of generations; for years. This was the first difference

observed, and I tried to demonstrate it by giving meas-

urements of successive generations of the different races.

But to the worker in the laboratory these differences are

evident without refined measurements; the student is at

82 THE AMERICAN NATURALIST [ Vou. XLV

once struck with the fact that one culture is formed of

individuals that are throughout and constantly larger

than those of another culture.

And here, in view of that extraordinary cry ‘‘no here-

dity without a correlation table’? (a ery that at once

annihilates most Mendelian evidence of heredity), it may

be well to define a little more precisely what is meant by

saying that the diverse sizes are hereditary in the differ-

ent races. It means that if you keep your different geno-

types side by side under precisely the same conditions,

you will find whenever you choose to examine and meas-

ure them, that each has a characteristic size, differing

from that of the others. If therefore you follow the

diverse lines from generation to generation you will get

a set of chains, each with links differing characteristically

throughout from the links of the other chains. It means

that it is possible to predict the diverse relative sizes that

will be found in the different races, and that when you

examine them a hundred generations later, you will find

the prediction correct. These striking facts are what are

meant by the statement that the diverse sizes are heredi-

tary in the different lines—and the way to determine

whether the statement is true or not is to examine the

lines from generation to generation to see if the state-

ment is verified. To neglect this obvious fact; to mix all

your lines together and then, in order to find out if size 1s

inherited, to laboriously work out coefficients of correla-

tion by refined biometrical methods—is like cutting serial

sections ten microns thick of an eel, in order to find out

whether it has an alimentary canal. Persons have been

known to so bedevil material with refined histological

methods as to quite miss the alimentary canal of an eel.

The way to see it is to open the animal up and take a look

atit. The way to see diverse genotypes is to isolate them

and look at them and measure them and compare them.

If the use of correlation tables should succeed in obscur-

ing these striking facts (as should not be the case with

proper handling) this would merely show the worthless-

* Compare Pearson, Biometrika, 1910, Vol. 7, p. 372.

No. 530] PURE LINES IN STUDY OF GENETICS 83 -

ness of this method of attempting to learn the important

biological facts under consideration.

2. Some of the genotypes show slight but constant

differences in structure, which I shall not dwell upon

here.*

3. They show most varied differences in their physio-

logical characters. These physiological differences may

go with differences in form and structure, or apparently

they may not—so that we find types that differ, so far as

detectable, only in physiological peculiarities.

This fact becomes of great practical importance for

all physiological investigations, as a few examples from

Paramecium will show:

(a) The races or genotypes differ in the conditions, both

external and internal, that induce conjugation. A worker,

using a certain strain, works out the conditions inducing

conjugation and gives precise directions for accomplish-

ing this. His colleague, with another strain, finds this

work all wrong, and the controversy on this ancient

question continues. One of my strains can be absolutely

depended on to conjugate monthly if certain definite con-

ditions are furnished; another under the same condi-

tions never conjugates; others show intermediate con-

ditions. These differences require no biometric methods

for their demonstration.

(b) Again, the genotypes differ in rate of multiplica-

tion; under the same conditions some divide once in

twelve hours; others once in twenty-four or more hours;

others have intermediate periods.

(c) The genotypes differ as to the conditions required

for their existence and increase. Several strains, out-

wardly alike, living in the same medium, are cultivated

side by side on slides, in the.usual hay infusion. One

flourishes indefinitely. Another multiplies for ten gen-

erations, then dies out completely, and this is repeated

invariably, no matter how many times we start anew our

“For a detailed, illustrated account ug “ characters, both structural

and ge pene of these races , see Jennings and Hargitt, ‘‘ Character-

isties of the Diverse Races of Peia, >” Journal of ‘Morpholo ogy, De-

cember, 1910

f

a

84 THE AMERICAN NATURALIST [Vou. XLV

cultures of this genotype. A third lives along in a sickly

way, barely maintaining its existence.

Thus we get in our laboratory striking cases of nat

ural selection between genotypes. To recall our com-

parison with human beings, if we could mix an entire

community composed homogeneously of, let us say,

Roosevelts, with another of copies of your ash man—

which would be likely to survive? If we place together

in the same culture two genotypes of Paramecium, as I

have many times done, almost invariably one flourishes

while the other dies out. This ruins many a carefully

planned experiment; it must take place on a tremendous

scale in nature.

What distinguishes the different genotypes then is,

mainly, a different method of responding to the environ-

ment. And this is a type of what heredity is; an organ-

ism’s heredity is its method of responding to the envir-

onmental conditions. Under a given environment the

genotype A is large, while the genotype B is small.

Under a given environment the strain C conjugates,

while D does not. Under a given environment the strain

E divides rapidly, F slowly or not at all. The various

strains thus differ hereditarily in these respects, and we

may say that the differences are matters of heredity.

And yet we can get these same contrasts within any

genotype (as our diagram illustrates), by varying the

environment. The genotype A under one environment

is large; under another it is small. Under one environ-

ment the type C conjugates; under another it does not.

Under one environment E divides rapidly ; under another,

slowly. / Are then size, conjugation and rate of fission

after all determined by heredity or by environment?

Such a question, when thus put in general terms, is

everywhere an idle and unanswerable one. All environ-

mental effects are matters of heredity when we compare

types differing in their reaction to the environment; all

hereditary characters are matters of environmental ac-

tion when we compare individuals of the same heredity

under effectively different environmental conditions.

No.530] PURE LINES IN STUDY OF GENETICS

A A i

B A |

| | , i 3 |

F E | E | E

Different Race Same Race

Same Environment Different Environment

DIAGRAM TO ILLUSTRATE THE RELATION OF HEREDITY TO ENVIRONMENTAL ACTION

IN DETERMINING CHARACTERS. xt.)

Heredity has a meaning only when we (explicitly or im-

plicitly) compare two concrete cases; when we say: To

what is due the difference between these two cases?

Otherwise we can demonstrate either that all character-

86 THE AMERICAN NATURALIST [Vou. XLV

istics are hereditary (as we heard maintained at Woods

Hole some summers ago); or, with Brooks, that there is

no such thing as heredity. If we always compare two

concrete cases, asking to what is due the difference be-

tween them, and remembering that a difference in hered-

ity means different response to the same environment,

we shall avoid these confusions, and shall find the con-

cept of heredity most useful.

Do hereditary differentiations ever arise within our

genotypes, so that from one genotype we get two? In

other words, do we get from a single type strains that

differ in their behavior under the same environment—

the differences persisting from generation to generation?

This is of course one of the fundamental questions. The

genotypes of Paramecium, like those of most other or-

ganisms that have been carefully studied, are singularly

resistant, remaining quite constant in most respects, so

far as has been determined. This is an example of what

gives the genotype concept its practical and theoretical

importance. This is what is meant by saying that selec-

tion and environmental action are usually without in-

herited effect within the genotype. To find differentia-

tions within the genotypes of Paramecium, we must

examine certain characteristics that are most delicately

poised in their responses to all sorts of conditions; such

is the rate of multiplication. Studying carefully this

most sensitive character, we find that differences do arise

within the genotype. Under given conditions, certain

rare individuals are found that divide more slowly than

usual, others more rapidly, and these differences are

perpetuated from generation to generation indefinitely.

How are these hereditary differentiations produced?

The origin of these differentiations is in Paramecium

as elusive as in most other cases where they have been

discovered. Apparently they arise in our organism as a

result of conjugation within the genotype. Certainly if

after an epidemic of conjugation within the genotype we

cultivate many isolated exconjugants, we find a certain

small number of strains that differ in their rate of fission

No.530] PURE LINES IN STUDY OF GENETICS 87

from that which is typical. But the experimental analy-

sis of this matter is still in progress, and conclusions

can not yet be drawn.

It is only in rate of multiplication that I have thus far

found hereditary differences arising within the pure line,

and these but rarely. But this encourages one to hope

that the same may be found for other characters when

these are extensively studied with sufficient minuteness.

The negative results thus far reached do not (as many

critics have pointed out) exclude the possibility that

rare cases of hereditary variation within the pure line

will yet be found. What the negative results have

demonstrated is that a very large share of the observed

variations in organisms are not hereditary, and that se-

lection based on these variations leads to no result—a

conclusion of such great importance as to make the pure

line work epoch-marking in character.

Finally, what happens when diverse genotypes mix in

conjugation? To my disappointment, I have found this

much more difficult to determine for the infusorian than

I expected. This is owing to the fact that the condi-

tions for conjugation differ in the diverse genotypes, so

that it is almost impossible to get them to conjugate at

the same time. Further, in the rare cases where two are

conjugating at once, the assortative mating discovered

by Pearl results in the two sets remaining separate.

Thus I have not yet been able to get crosses between two

genotypes whose characteristics are known beforehand;

and this will be necessary before a study of inhoritaned,

exact in the modern physiological sense, can be made.

On the other hand, it is possible to get conjugations in wild

populations that include many genotypes, and to com-

pare the results with conjugations where but a single

genotype is involved. Certain most interesting results

appear. In these conjugations of mixed populations, a

great number of diverse combinations are produced ; the

variability increases greatly, in size and in other re-

spects. Numbers of the strains produced die, or multiply

so slowly that they have no chance in competition with

88 THE AMERICAN NATURALIST [Vou. XLV

those that are strong and multiply rapidly. Thus many

of the combinations produced are canceled; only the

strongest combinations survive. We have then on a

most extensive scale an operation in natural selection

and the survival of the fittest; the production of many

combinations, some of which survive, while others fail.

As already set forth, there is some indication of the same

process in the case of conjugation within the genotype.

At our last meeting I tried to summarize the facts as to

the relation of genotypic investigation to selection; it

turned out that much which had been deemed a progres-

sive action of selection was not such; and up to that time

the action of selection in modifying genotypes had not

been demonstrated. Similarly, I had earlier summar-

ized the facts regarding selection in behavior, showing

that it there plays a large part. I have hence suffered

the peculiar fate of being belabored as an anti-selectionist

in genetics, while subjected in the field of behavior to

rough treatment as the champion of selection. What I

tried to do in both cases was, to determine how far we had

actually seen the effectiveness of selection—holding this

question quite apart from what we believe must occur, or

believe will be found to occur when we have seen it. It

appeared clear, and still appears clear, that a very large

share of the apparent progressive action of selection

has really consisted in the sorting over of preexisting

types, so that it has by no means the theoretical signi-

ficance that had been given to it. When operating on a

single isolated type it appeared that the progressive

action of selection had not been seen. These are facts of

capital importance to the experimenter; besides their

theoretical significance, they open to each of us the oppor-

tunity to direct our efforts upon precisely this point, and

so perhaps to be the first to see examples of this funda-

mental process not yet seen. I hoped to accomplish this

myself, but after strenuous, long-continued, and hopeful

efforts, I have not yet succeeded in seeing selection effec-

tive in producing a new genotype. This failure to dis-

cover selection resulting in progress came to me as a

No.530] PURE LINES IN STUDY OF GENETICS 89

painful surprise, for like Pearson I find it impossible to

construct for myself a ‘‘philosophical scheme of evolu-

tion’’ without the results of selection and I would like to

see what I believe must occur. It is therefore with some

pleasure that I am able to record for Paramecium this

extensive operation of selection among the diverse exist-

ing lines, and particularly in this extensive production of

new combinations at conjugation, with cancellation of

many of the combinations. It would seem that the

diverse genotypes must have arisen from one, in some

way, and when we find out how this happens, then

such selection between genotypes will be all the selection

that we require for our evolutionary progress. What I

hope, therefore, is that some one on our program, more

fortunate than myself, will be able to record seeing the

actual production of two genotypes from one, or the

transformation of one into another, by selection, or in any

way whatever.

Yet even if this is done, we shall make the greatest

possible mistake if we therefore conclude that the exist-

ence of genotypes is unimportant, and throw the matter

aside ; for work with a mixture of unknown genotypes will

always give confused and ambiguous results, whose signi-

ficance no one can know. If on the other hand we work

with single genotypes, or with known combinations of

them, we shall understand what our results mean. And

this applies to work in other fields of biology as well as to

genetics,

SOME EFFECTS OF TEMPERATURE UPON

GROWING MICE, AND THE PERSISTENCE

OF SUCH EFFECTS IN A SUBSE-

QUENT GENERATION?

DR. FRANCIS B. SUMNER

Woops Hote, Mass.

I must preface my remarks by an apology for coming

before you with some results which have already been

published pretty fully within the past year.? My appear-

ance here may seem the more unwarranted in view of the

limited amount of evidence which I am about to offer

upon those subjects which form the focus of attention at

this meeting, namely heredity and evolution. However,

aside from the fact that I am acting at the instance of our

president, I will say two things in my own defense.

First, the results which I offer, meager as they doubtless

are, appear to be the only ones of just this sort which are

in evidence at present. And secondly, I am bold enough

to believe that I have developed a promising method of

attacking a few of the many knotty problems which are

bound up together in the time-honored question: Are

‘Read before the American Society of Naturalists, December 30, 1910.

? (í Some Effects of External a upon the White Mouse,’’ Journal

of Experimental Zoology, August, 1909. ‘‘The Reappearance in the Off-

spring of Artificially Produced piena Modifieations,’? AMERICAN NAT-

URALIST, January, 1910. ‘‘An Experimental Study of Somatie Modifica

tions and their Reappearance in the Offspring,’’ Archiv fiir Entwicklungs-

mechanik der Organismen, June, 1910.

*Since writing this statement, I have received Semon’s highly interest-

ing paper, entitled ‘Der Stand der Frage nach der Vererbung erworbener

Kigenschaften’’ (Fortschritte der naturwissenschaftlichen Forschung, Bd.

TI, 1910). From this I learn that some of the more important features of

my results have been obtained by Przibram, in the course of experiments

upon rats, conducted at about the same time as my own. I have not yet

seen Przibram’s own report of his work. This confirmation will, I trust,

dispel any doubts as to the statistical aM of my own figures, what-

ever interpretation we may choose to give them.

90

No. 530 | TEMPERATURE ON GROWING MICE 91

acquired characters inherited? It is my hope to convince

you that the method which I have employed conforms to

certain a priori requirements, on the one hand, and, on the

other hand, is workable in practise. That my results are

not thus far more imposing is due, I think, to no defect in

the method itself, but to the limitations which encompass

a solitary investigator, deprived of some of the generally

acknowledged desiderata for successful work in animal

breeding, such, for example, as assistants, funds and ade-

quate equipment.

As to the logical requirements for such a test—to begin

with, what is it that we are going to test? The ‘‘inherit-

ance of acquired characters’’?—yes and no. First of all,

that threadbare expression itself must be relegated to

limbo where it belongs. For, not only does it fail to indi-

cate with any precision the subject-matter of our inquiry,

but historically the expression has been applied to a wide

range of phenomena, real and alleged. Some of these we

now know to be fictitious; others, on the contrary, are

acknowledged facts; while others yet are more or less

debatable. It is with the debatable group, of course, that

we are here concerned. But, even among these, we en-

counter not one problem but many. Suppose, then, that

we drop all vague generalized expressions and consider

one more or less restricted problem: Are specific struc-

tural effects, resulting from the action of external condi-

tions upon organisms of one generation ever repeated in

the next generation under such circumstances that the

immediate and parallel modification of the germ-cells

may not be invoked as an explanation? Under ‘‘specifie

structural effects,” I do not wish to include general con-

ditions of health, metabolism, ete.

What are some of the necessary conditions for a fair

test of this question? To begin with, we must effect our

modifications in the first generation. And since these

modifications, if repeated at all, will probably reappear

in a much-diminished degree, it would seem far prefer-

able to select characters which lend themselves readily

92 THE AMERICAN NATURALIST [ Vou. XLV

to accurate measurement. Qualitative differences, such

as those of color or of physiological reactions, do not

seem well adapted to such experiments, although they

have commonly been the ones dealt with in studies of this

sort.

In the second place, we must choose such an organism

and such a physical agency that the latter may act upon

the former without immediately influencing the germ-

cells. This would seem to rule out of consideration as

really crucial tests of this problem all experiments, how-

ever instructive otherwise, in which modification has been

brought about through the influence of foods, unusual in

amount or in character. For the effect of these upon the

parent body is, of course, a chemical one, and the specific

substances responsible for the modifications are presum-

ably free to enter the germ-cells. The experiments of

Arnold Pictet upon lepidoptera and of Houssay upon

fowls are to be recalled in this connection. Similar con-

siderations apply with equal force to any results from

experiments in which invertebrate animals or ‘‘cold-

blooded’’ vertebrates have been influenced by tempera-

ture. The recent work of Kammerer upon lizards* and

that of various investigators upon butterflies and moths

occur to us at this point; likewise certain features of

Tower’s work on Leptinotarsa. In such cases, by pretty

general consent, we have to do with an ‘‘immediate effect

upon the germ-plasm,’’ and not with transmission at all.

Later, I shall inquire a little into the validity of this

assumption.

~ In the meantime, I will point out that for certain

classes of animals this objection cannot be raised, at least

in its original form. I refer to the so-called ‘‘warm-

blooded’’ ones. Iam not very well versed in that branch

of physiology which deals with temperature regulation,

but the published evidence which I have examined seems

to show that mammals normally undergo but slight fluc-

tuations of body temperature as a result of even very

* Archiv fiir Entwicklungsmechanik der Organismen, September, 1910.

No.530] © TEMPERATURE ON GROWING MICE 93

considerable changes in the penparainre of the surround-

ing atmosphere.®

Assuming, provisionally, the truth of this proposition,

we may discount in advance the objection that the germ-

cells of a mammal may be influenced by differences of

temperature as such. If these differences affect the

germ-cells at all, and it is reasonable to believe that they

may do so, they must act upon them indirectly.* I shall

revert to this point again shortly.

_ As some of you may perhaps already know, I have

succeeded for several years past in producing very

decided quantitative differences in certain of the external

parts of mice through the action of widely differing tem-

peratures. ... (This part of the discussion has been

omitted in the printed report, since the results in ques-

tion have already been fully published.)

In experiments such as those which I am describing, it,

is obviously impossible to subject a single individual to

both extremes of temperature during growth, and to com-

pare the differing effects of these upon structure. We

therefore, of necessity, resort to a comparison of aver-

ages, based upon as many individuals as possible. If

each of the contrasted groups is sufficiently large, and if

its members have been taken at random, the presumption

*Przibram found that the body temperature of his rats was somewhat

C. This |

raised when kept in a room at 30° to 35° ast was, however, con-

siderably higher than the me n temperature of my own warm m, a

e

his experiments. (See Semon, op. cit., pp. 45, 46.) On the other hand;

Pembrey (Journal of Physiology, 1895) found that the body temperature

of mice did not rise appreciably above the ea when the animals were

kept at a temperature of 29.5° or even 32.5° C. for an hour or more.

effects of a more prolonged stay were not determined. I have myself

Heese commenced experiments with mice, using a special clinical ther-

meter made for the purpose. I have already (January 21) shown pretty

Saian that mice may ws almost precisely the same rectal tempera-

ture at —'6° C, as at + 30°

e is true even Oy tunndbatty: ritak than temperature per se, is

the factor ahia concerned in these modifications. As "o in my T

paper (1909), the relative humidity of my heated room wa very m

lower than that of the unheated room. Thus far I have not PPa

the effects of these two factors.

94 THE AMERICAN NATURALIST [Von XLV

is that the mean potential (that is to say, congenital)

value of every character is about the same for the two

lots. I fully realize that the study of genetic problems by

the use of mass averages has recently received a decided

set-back, largely through the labors of some of those who

have contributed to our present program. But until

some one is ingenious enough to produce a strain of par-

thenogenetic or self-fertilizing mice, I fear that my only

practical. method of procedure in these experiments is to

deal with mass statistics based upon ‘‘heterozygous”’

stock.

It must also be pointed out that the technique of the

problem which I am discussing is inevitably different

from that involved in the endeavor to find, or to produce,

‘‘mutations’’ or single abrupt deviations from the parent

stock, which appear at once in full force, if they appear

at all, and thereafter breed true. On the contrary, the

distribution of the lengths for the tail, ear and foot,

within each of the temperature groups in my experi-

ments, appears to follow the normal probability curve,

just as in the case of the so-called ‘‘fluctuating varia-

tions,” whose heritability is nowadays so much in

question.

In the splendid paper of Professor Johannsen, to which

we listened yesterday, occurs the following statement:

‘as yet no experiment with genotypically homogeneous

cultures has given any evidence for the Lamarckian view,

the most extreme ‘transmission’-conception ever issued.”’

Leaving aside for the time being the question whether

results such as mine, even when every possible defect of

technique has been eliminated, are to be regarded as

‘fevidence for the Lamarckian view,” let us consider for

a moment whether the fact that I have not myself found

it practicable to use ‘‘genotypically homogeneous cul-

tures’’ does, in reality, invalidate the evidence which I

offer. Ay y Professor Johannsen would hold this

to be true. Bo far as I can see myself, the only difference

between results from pure and from mixed lines in the

No.530] © TEMPERATURE ON GROWING MICE 95

present case would be this. Individuals belonging to a

single pure line would probably respond with much

greater uniformity to the effects of an environmental

change than would those belonging to a composite stock,

consisting of a number of lines. It is quite conceivable

that among these last some would respond in a much

greater measure than others. Or indeed some might not

be affected at all. But here the much-scorned ‘‘mass

statistics’? would reveal the mean tendencies of the two

lots, and the resulting data, though confessedly capable

of further analysis, would be none the less valuable. If

it be objected that the differences between the two aver-

ages may be due to the presence in one or both of the con-

trasted lots of a few ‘‘mutants,’’ while the remaining

individuals may not have been affected at all, I will only

point out, as above, that the frequency distributions are

directly opposed to such an assumption.

Having produced modifications of the sort mentioned,

it remained to be seen whether these effects persisted

beyond the generation immediately influenced. . . . (This

part of the discussion, including an account of the method

employed, the results, and certain of the possibilities of

interpretation, I have thought it best to omit here, in view

of the fact that I have covered practically the same

ground in statements already published. I will merely

note that the offspring of warm-room and cold-room mice,

although themselves reared under identical temperature

conditions, presented differences of the same sort as had

been brought about in their parents through the direct

effect of temperature, viz., differences in the mean length

of tail, foot and ear.)

There remain two principal alternative explanations,

which are not wholly distinguishable from one another,

and neither of which admits of being stated except in

rather vague terms.

One of these is the assumption that the changes under-

gone by the parent body are in some way registered in the

germ cells, so as to be repeated, in a certain measure, in.

96 THE AMERICAN NATURALIST — [Vou. XLV

the body of the offspring. This conception has taken

various forms, commencing with Darwin’s hypothesis of

‘‘nangenesis.’’ The same general view has recently been

restated in chemical terms, and in a manner which is

perhaps far less shocking to our common sense.

The other alternative is that of a ‘‘ parallel induction”’

or ‘‘simultaneous modification of the germ-plasm,’’

through the direct action of the modifying agent. This

explanation, as we all know, has been freely used by

Weismann and others to account for a considerable range

of phenomena, notably the persistence of temperature

effects in a second generation of butterflies. The phrase

has indeed become so familiar through long repetition

that few of us stop to consider just what it implies.

‘Parallel modification of the germ-plasm?’’ How can

the unformed material of the germ cells be modified in the

same manner as certain groups of somatic cells—say in a

butterfly’s wing—even by an all-pervading influence like

temperature? This is obviously not what is intended.

What we mean, concretely stated, is this: the germinal

matter is so affected by the temperature that, after some

hundreds or thousands of cell generations, certain of the

resulting cells will show peculiarities in their pigment-

producing powers of the same nature as those which

arose directly in the somatic cells of the parent. And a

most curious feature of this coincidence is that these

modified cells are situated in precisely the same parts of

the body in the one case as in the other.”

Thus do these very simple explanations have a way of

losing their simplicity when examined critically. In the

present instance, the hypothesis stated may, for all we

know, be the one that most nearly represents the truth.

But it should be stated frankly, in all its complexity, and

not palmed off upon us as a readily intelligible hypoth-

esis, which relieves us of the necessity of adopting an

‘‘inconceivable’’ one such as that of pangenesis.

* Weismann’s ‘‘determinant’’ hypothesis offers at least a formal solution

of this difficulty, but I think that most biologists will agree with me that

the solution thus offered is almost wholly a formal one.

No.530] TEMPERATURE ON GROWING MICE 97

In the case of a warm-blooded animal, of course, such

an explanation as the foregoing could not be offered with-

out still further modification. It might be conceded that

temperature, as such, could not affect the germ-cells to

any appreciable extent. But it might, on the other hand,

be contended that the effects of temperature, even upon

the parent body itself, may not be direct, but may be due

to the formation of specific chemical substances, which,

through the medium of the blood, may be supposed to

simultaneously influence the body and the germ-cells.

Thus we should, after all, be invoking a ‘‘simultaneous

modification of the germ-plasm,’’ as in the case of cold-

blooded animals.

Such a conception, vague as it is, has certain decided

elements of strength. Let me point out, however, as I

have already done more than once, that any such chemico-

physiological mechanism as is here assumed would be of

nearly or quite the same value for evolution as the

‘‘inheritance of acquired characters’’ in the old sense.

An interpretation of this sort might ‘‘save the face’’ of

certain speculative students of heredity, but the differ-

ence between the two views would have little but academic

interest.

At the present time, I am continuing these experiments

with mice, and am not only using much larger numbers

than hitherto, but am resorting to several variations of

the original theme, by which I hope to reduce the number

of possible interpretations to a minimum. A friend wrote

to me recently, wishing me no end of ‘‘good results, not

Lamarckian.’’ This doubtless represents the attitude of »

a large number of persons toward the whole subject. By

many, anything with a taint of ‘‘Lamarckism’’ about it

would seem to be, ipso facto, beyond the pale of legitimate

scientific investigation, belonging rather to the same cate-

gory as pre-natal influences, telepathy and the ‘‘border-

land’? phenomena of psychical research. But the dawn

of better times is already with us.

In conclusion, let me state that my own attitude toward

98 THE AMERICAN NATURALIST [ Von. XLV

this group of problems is one of indecision. If I confess

to you, as I am bound to do, that positive results from my

own experiments will give me far greater satisfaction

than negative ones, this is chiefly because negative results

commonly prove nothing. The question would be left

very nearly as it was before. This, of course, constitutes

a serious defect in my own vaunted method of attacking

the problem, a defect which it shares, however, with any

other which could be devised. But any results are better

than no results, and these problems seem worth afar more

thorough testing than they have yet received. The pres-

ent experiments ought, as Professor MacDougal has

pointed out, and the author keenly realizes, to be sub-

jected to various checks and controls, and to be continued

through a considerable series of generations. It is my

own fervent hope to be able to carry out such a program.

* Presidential address before the American Society of Naturalists, read

at Ithaca, December 29, 1910.

THE MENDELIAN RATIO AND BLENDED IN-

HERITANCE!

SHINKISHI HATAT

THE Wistar INSTITUTE or ANATOMY

Tue indefatigable efforts of neo-Mendelists have suc-

ceeded in bringing numerous cases of inheritance, which

had previously been considered incompatible with Men-

del’s law, into their domain by widening the original

limitations. We still have. many instances such as

blended inheritance which can not apparently be harmon-

ized with the law of Mendel. Recent experiments which

demonstrate the existence of various degrees of domi-

nance as well as the mutability of the determinants in

their behavior, suggested to the writer that various

forms of inheritance might be considered as degrees of

modification of the law of Mendel. With this view in

mind, I have attempted to obtain some general expres-

sion for the underlying principle of the law of inherit-

ance by which means Mendel’s original law may possibly

be theoretically connected with the other cases. In fact,

I was compelled to pursue this investigation in connec-

tion with my own experiments on the inheritance of the

weight of the central nervous system, though this is not

yet ready to present at this time.

In carrying out this investigation, I have assumed that

the germ plasm is composed of many factors, the true

nature of which is unknown, but which in one way or

another determine the characters in the offspring. It is

these hypothetical factors which are here provisionally

called determinants. With this understanding, we ma

now proceed to the argument. i

Suppose a gamete of one parent after the reducing

division contains n determinants, the whole group of

t Read before the American Society of Naturalists, December 30, 1910.

= 99

100 THE AMERICAN NATURALIST [ Vou. XLV

determinants being designated p, and the gamete of

another parent also contains after the reducing division

n determinants, the whole group being designated q.

Then in the first hybrid zygote (F,) there will be con-

tained at the time of the union of the gametes 2n determ-

inants. As we know, rearrangement takes place during

the maturation of the germ cells and we assume this

rearrangement to involve a random sampling by which

n determinants are taken from the group of 2n. From

the theory of probabilities we find that n, n— 1, n— 2

. determinants of either parent contained in the

gametes of F, are proportional to the successive terms

of the following series:

p+ np"—'q 4 nO) pig a n(n - oa oo es 5 ee ie ee a )

The same phenomenon e in the gametes of the

other hybrid parent (F,) and since the gametic consti-

tution of the two hybrid parents is assumed to be identi-

cal with respect to the distribution of determinants (1),

the frequency of the various combinations of the de-

terminants in the second hybrid offspring (F,) will be —

given by the square of (1) or

e 2 r n(n — 1)(n — 2)

T ar ao

2

(r m - Eri .) (2)

which may also be written as follows:

(p? + 2pq +a)".

This series, or the square of the binomial series, is

then the most general expression for the gametic com-

position of any hybrid arising from a combination of p

and q determinants and may therefore be considered as

the underlying principle of any law of inheritance where

the idea of determinants is used.

It is evident that since the somatic characters in ques-

tion depend entirely on the behavior of the determinants,

the relative frequency of various zygotes, as well as the

character of the zygotes, depends on whether p or q de-

No. 530] THE MENDELIAN RATIO 101

terminants are related as dominant and recessive, re-

spectively, or whether they blend.

Suppose p is recessive and q is dominant in the Men-

delian sense, we at once obtain from (2) the general

expression for the alternative inheritance or

(RR + 2DR + DD)”

where n refers to the number of allelomorphic pairs of

characters, and the expansion gives a strict Mendelian

ratio for any number of allelomorphic pairs of char-

acters.

On the other hand, if we consider that p and q determi-

nants blend with an equal intensity the series (2) will

give all grades of hybrid characters between the two pa-

rental types, the frequency of which is proportional to

the successive terms of a symmetrical point binomial

curve, and the maximum frequency will be associated

with the midparental types (case of equipotency).

Castle’s (’09) experiments with the length of the ear of

rabbits illustrates this case.

Again let us suppose that p and q determinants blend,

but with unequal intensity. According as p or q is pre-

potent, the zygote will resemble more closely one or the

other parent. The frequency of each type of zygote

again will be represented by the symmetrical point bi-

nomial curve. Thus the present series (2) represents

both alternative and blended inheritance according to

the behavior of the determinants.

The fact just mentioned, that the expressions for both

blended and alternative inheritance are obtained from

the same series which represent the gametic composition,

suggests that we may possibly obtain cases of blending

in character which normally follow the law of the alter-

native inheritance, and vice versa, and further we may

even obtain both blended and alternative inheritance in

the same offspring by subjecting the hybrid parents to

different conditions, provided by such treatment we can

modify the behaviors or functional activity of the de-

102 THE AMERICAN NATURALIST [Vou. XLV

terminants, since as soon as the behavior is altered, we

at once obtain from the series (2) another type of in-

heritance.

Although we have no clear direct evidence which

demonstrates an occurrence of such extreme modification

in the behavior of determinants, nevertheless the possi-

bility of such an event is amply suggested by the recent

experiments. For instance Tower (°’10) has shown not

only a reversal of dominance and apparent failure of

segregation by merely modifying the environment of the

beetles, but also a case in which the same parents pro-

duce offspring, some of which follow the law of Mendel

while others show entirely different behavior with re-

spect.to dominance and segregation. Tennent (’10) was

able to obtain from a cross of Hipponoë esculenta with

Taxopneustes variegatus, reversal of dominance by de-

creasing the alkalinity of the sea water. Numerous

samples of this sort can easily be found in the recent

literature.

Whatever be the real condition or conditions which

control the behavior of the determinants, one point is

clear from the above, that the determinants are not im-

mutable in their behavior, but subject to modification.

This fact naturally leads us to think that we may obtain

various forms of inheritance which are more or less dif-

ferent from the type form according to degree of func-

tional modification. When a modification is maximum,

we may even obtain a case of blended inheritance in a

character which normally follows the law of alternative

inheritance, or vice versa.

The facts mentioned above then indicate that our de-

duction from the properties of the formula is not at all

improbable.

Again the properties of the formula suggests that we

can theoretically connect cases of blended inheritance

with those of alternative inheritance by the mere as-

sumption that p or q fails to dominate either completely

or incompletely. Since as we have shown by the degree

No. 530] THE MENDELIAN RATIO 103

of dominance, the formula reduces to either equipotent

or prepotent blending inheritance. From this stand-

point we may consider that blending inheritance is a

limiting case of alternative inheritance where either —

dominance is absent (equipotency) or is imperfect

(heteropotency). If this hypothesis is accepted, then

Mendel’s law of alternative inheritance may be taken as

the standard, and all cases referred to it or blending in-

heritance (though by this some more important features

of inheritance are not suggested) may similarly be made

the standard, the Mendelian ratios then becoming a

special case.

In this connection Professor Davenport’s (’07) view

on the law of potency is of great interest. As his view of

potency is so important, and especially as it clearly ex-

plains the relation between Mendelism and cases con-

sidered to be non-Mendelian, I shall quote his words at

some length.

After quoting various cases of inheritance, Professor

Davenport says:

_ Taking all cases into account, it is clear that Mendel’s law does not

cover all; and if not, it must be a special case of a more inclusive law.

Can we find a more general expression for the inheritance of charac-

teristies which will cover all these cases? I think we can and that it

may be called the law of potency. At the one extreme of the series we

have equipotent unit characters, so that when they are crossed, the

offspring show a blend, or a mosaic between them. At the other extreme

is allelopotency. One of the two characteristics is completely recessive

to the other. Between the two extremes of equipotency and al lelopo-

tency lies the great mass of heritable characteristics which when opposed

in heredity, exhibit varying degrees of potency. This sort of inherit-

ance may be called heteropotency.

Thus Professor Davenport shows also that Mendelian

dominance is a particular case of potency, allelopotency,

though he did not state that blending inheritance is a

limiting case of Mendelism.

Whether a new expression ‘‘the law of potency”

should be introduced as Professor Davenport has sug-

gested, or whether the various potencies may be consid-

104 THE AMERICAN NATURALIST [ Vou. XLV

ered as a limiting case of Mendel’s law of alternative

inheritance, thus saving the original name, is a matter

for later decision, though the latter name seems to me

` more appropriate to retain owing to the fact that the

phenomenon of segregation, most important of all, had

been first stated by Mendel.

Let us now consider a limiting case of our formula (2)

when the values of. n (number of allelomorphic pairs of

characters) increase. In the typical Mendelian ratio,

the relative frequency of the various zygotes with re-

spect to any given visible character is proportional to an

expansion of (1+ 3)" which is the same as (1/4 + 3/4)"

if we consider the relative values of the frequencies.

Thus in all known cases of the inheritance, we have to

deal with an expansion of (r -+ s)” where r+ s=1. A

concise mathematical formula which represents a limit-

ing case of the binomial series arising from an expansion »

of (r + s)” will be very useful, especially when we are

dealing with a quantitative measurement such as weight,

length, area, volume, etc., since in these cases the values

of the variates will be graded. Further, the theoretical

frequency corresponding to each variate when the value

of n becomes very large, can best be determined from

such a mathematical expression which represents a limit-

ing case.

Without going into any detail of the mathematical

treatment, it will be seen that we obtain two forms of

expression according as r= s or rs. The former will

be represented by the normal probability curve and the

latter by a limiting case of a skew binomial curve. For

representing a skew binomial curve we can best use

DeForest’s formula (Professor Pearson’s curve of type

3). It may be useful to the reader to know that De-

Forest’s formula degenerates into the normal probability

curve as its simplest form, as will be seen below.

DeForest’s formula (Hatai: 710) is usually written in

the following form:

No. 530] THE MENDELIAN RATIO ~ 105

1 X a?b—1

= ———_| ] aes eae

A a ea +e) a

where

1

k= 1 May aor For

12a%b ™ 288(a°b)?

a =— quotient of twice the second moment divided

by the third moment.

b — second moment.

Writing c for

1

ky 2mb

we have

log (2) = (e0 — 1) log (1 +3)

æ i/Ææ\ that? 1oy"

= (ab — Dia- la T 1 -a a |e

a x? 1 x a eae | ey

--35+(35- )a-(Ge-3) ab

g l ey

kab 8 [Nag

Since for a vanishingly small value of the third moment,

ab will be a very large number, consequently #/ab will

be infinitesimal. Thus neglecting all terms in which x/ab

is factor, we have

Restoring the value of C and remembering that for large

values of ab, k reduces to unity, we finally have

which is the familiar formula for the normal probability

curve.

From the above it is clear that DeF orest’s formula and

its limiting case represent the frequency distribution of

the zygotes, whether we are dealing with alternative or

106 THE AMERICAN NATURALIST [ Vou. XLV

blended inheritance. One, however, must not be misled to

conclude that continuous variation necessarily means

failure of segregation, since on the contrary apparent

continuity may be a resultant of combinations of various

segregating characters. Whether or not given data indi-

cate a segregation, may be variously tested by some other

means according to the nature of the experiment.

From the above we draw the following conclusions:

1. The series obtained from the square of the binomial

expresses the distribution of determinants for both alter-

native and blended inheritance.

2. Blended inheritance may be considered to be a limit-

ing case of alternative inheritance where dominance is

imperfect. Thus Mendel’s law of alternative inheritance

may be considered as the standard and all other cases

referred to it.

3. DeForest’s formula with its limiting case ade-

quately represents frequencies of all known cases of

inheritance when the number of allelomorphic pairs of

characters is large, especially when quantitative meas-

urements are considered.

LITERATURE CITED

1909. Castle, W. E. Studies of yong in Rabbits. Pub. of the

; Carnegie Inst. of Washington, No. 114, pp. 9-68.

1907. Davenport, C. B. Heredity and Mendel’s Law. Proc. of the Wash.

Acad. of Sciences, Vol. 9, p. 179.

1910. Davenport, C. B. e Imperfection of pR and some of its

Consequences. Am. Naturalist, Vol. 44, pp. 150-155.

1910. Hatai, §. DeForest’s Formula for ‘‘ An Unsymmetrical Probability

Curve.’’ Anat. Rec., Vol. 4, No. 8, pp. 281-290.

1910. Tennent, D. H. The Dominance ps E or of Paternal Char-

acters in Echinoderm RIET . f. Entwicklungsmechn. d.

O

1910. Tower, W. L. The Determination of Dominance and Modification

of Behavior in Alternative (Mendelian) Inheritance, by Conditions

Surrounding or Incident upon the Germ Cells at Fertilization. Biol.

Bull., Vol. 18, No. 6, pp. 285-352.

DATA ON THE RELATIVE CONSPICUOUSNESS

OF BARRED AND SELF-COLORED FOWLS!

DR. RAYMOND PEARL,

MAINE AGRICULTURAL EXPERIMENT STATION

I. Puystcan Data

Tue purpose of this note is to put on record a rather

striking physical fact, and to discuss briefly its biological

significance. Some two years ago Davenport? published

a short note regarding the relative number of self-colored

and of ‘‘penciled or striped’’ chicks killed by crows one

afternoon, at Cold Spring Harbor. The rather striking

result was that out of 24 birds killed, only one was other

than self-colored. The communication closes with the

following words: ‘‘This fragment, then, so far as it

goes, indicates that the self-colors of poultry, which have

arisen under domestication, tend to be eliminated by

the natural enemies of these birds, and the pencilled birds

are relatively immune from attack because relatively

inconspicuous.’ |

Some photographs taken on the poultry range of the

Maine Experiment Station this past summer illustrate

this point made by Davenport as to the relative conspic-

uousness of self-colored birds in so striking and com-

vlete a manner as to warrant their publication and a

critical discussion of their significance. These photo-

graphs were made without any thought whatever at the

time that they were going to bring out the relative con-

spicuousness of different plumage patterns. Indeed, it

was not realized that they did so until the finished prints

were given to me by the station photographer, Mr. Roy-

1 Papers from the Biological Laboratory of the Maine Experiment Sta-

tion, No. 23.

* Davenport, C. B., ‘‘ Elimination of Self-Coloured Birds,’’ Nature, Vol.

78, p. 101, 1908.

107

108 THE AMERICAN NATURALIST [ Vou. XLV

i Photograph of a Golden Pencilled Hamburg g- Practically. a solid

colored bird (red on body, black tail). The few barred feathers which the

of this variety has are covered by solid colored feathers. In this picture one

barred feather shows in the region of the saddle. The wind had displaced this

feather.

den Hammond, to whom I am indebted for developing

and printing these pictures. As a matter of fact the

four pictures which accompany this note were taken for

the purpose of (a) testing a then new camera as to its

usefulness in obtaining pictures to form part of a per-

manent record system in poultry-breeding experiments,

and (b) to get photographic records of certain particu-

lar birds of interest from one standpoint or another.

All the exposures were made by the same person (the

writer) on the same afternoon and within an hour of

each other. It was on a cloudless afternoon early in

August, and the light conditions, shutter-opening, speed,

and diaphragm opening were constant for all of the pic-

tures. What differences appear in the pictures, then,

are such as are referable to the different color patterns

of the birds, when seen under the light conditions and

against the kind of background which obtained in this

case.

No. 530] RELATIVE CONSPICUOUSNESS OF FOWLS 109

Fic very dark, practically solid black Fə g from the cross Cornish

Indian pute Fı 9 from Cornish Indian g x Barred Rock Q.

From these photographs the following poimia are to be

noted :

1. As compared with self-colored birds the barred in-

dividuals obviously are relatively much less conspicuous,

when under the same light conditions, and when seen

against the same kind of a background. The pictures of

the barred birds (Figs. 3 and 4) are not, to be sure, like

the ‘‘puzzle’’ pictures of supposedly protectively colored

organisms, which one sometimes sees, where it is exceed-

ingly difficult to distinguish the animal from the back-

ground at all. In both Figs. 3 and 4 it is easy enough

to see the bird, but at the same time these birds are

obviously much less conspicuous than those shown in

Figs. 1 and 2.

2. This inconspicuousness is equally marked whether

the barred bird is in the bright sunlight (Fig. 3) or in

a relatively deep shadow (Fig. 4).

3. These pictures furnish objective and unbiased phys-

110 THE AMERICAN NATURALIST [ Vou. XLV

2 ate cross-bred chick. .Sex 9. Produced by mating Fi

barred ‘croes-breda inter s$

ical evidence regarding the relative conspicuousness of

two types of plumage pattern.

II. Dara on tHE Bronocican VALUE or THE [NCONSPIC-

UOUSNESS OF THE BARRED PATTERN

The physical fact set forth above is obvious: barred

chickens are clearly less conspicuous than self-colored

when seen against the background of grass on the range

where they live. Has this physical fact any biological

significance? Are the barred birds, by virtue of the

possession of this color pattern, at any advantage in

the struggle for existence? Is their relative inconspic-

uousness any real protection against their natural ene-

mies? It is the purpose of this section of the paper to

present some numerical data regarding this matter.

The only evidence which exists in the literature on this

problem, so far as poultry is concerned, consists in the

admittedly fragmentary statistics presented by Daven-

port, which have been cited above. It should be pointed

No. 530] RELATIVE CONSPICUOUSNESS OF FOWLS 111

F ure Barred Plymouth Rock Q, with barring of fine quality from

the fyn i Spd It is to be noted that the bird in this figure is in the

shadow of a T in contrast to that shown in Fig. 3, which is standing in

the bright s

out that Davenport’s data are fragmentary not alone in

respect to the small number of deaths (eliminations in

the technical sense) involved, but also because these

deaths were due to but a single one of the natural ene-

mies of poultry, namely the crow. There are, of course,

many others. Under the conditions prevailing on or

about the poultry plant of which the writer has charge

the following animals are regular or occasional destroy-

ers of young chicks: Rats, skunks, foxes, crows, hawks,

cats.’

In different seasons the relative importance of these

different enemies varies. Thus in the breeding season of

1908 many birds were killed by foxes. In 1909, the year

“To this list one feels tempted to add that species of vermin which is

in some respects the worst which attacks a poultry plant, namely the thief,

but fortunately the range was free from his depredations in 1909.

112 THE AMERICAN NATURALIST [ Vou. XLV

for which statistics are given below, not a single bird was

killed by a fox so far as is known. Similarly in 1909 no

birds were killed by skunks. In 1910 a skunk succeeded

in getting into a house one night and killed a number of

birds. On the Maine Station plant normally predaceous

birds undoubtedly rank first in destructiveness. This is

probably quite generally true of poultry plants, though

because of the fact that the loss is distributed so evenly

over the whole season the importance of this class of

enemies is apt to be underrated. Next to predaceous

birds stand rats, under our conditions. An important

point to be noted is that on the plant under discussion

here all killing of chickens by rats is done in the daytime.

Rats burrow in the ground under the houses, and then

when the chicks are playing about a rat will dash out,

seize a chick and carry it back to the burrow. It is not

an uncommon occurrence for a rat thus to kill as many

as 12 chickens within the space of an hour. With rare ex-

ceptions we never lose any chickens at night except those

taken by thieves. The chicks are shut and locked in rat

and (usually) vermin proof houses at night. Occasion-

ally, as noted above, a skunk is able to effect entrance

into a house. This, however, did not happen in 1909, the

year which furnished the statistics given below. It

should be clearly understood that in the statistics which

follow all ‘‘eliminations’’ occurred in the daytime, when

color and pattern might presumably be of some signifi-

cance.

It is my purpose to present some statisties, involving

a relatively large number of individuals, regarding the

relation of color pattern to the elimination of chickens

by all of these natural enemies taken together. These

statisties cover the hatching season of 1909 in which

chickens were on the range, and subject to the attacks

of enemies, from about April 1 to October 1. Birds of

all colors and patterns ran together on the same open,

turf-covered range, and, without regard to color or pat-

tern, all were equally exposed to attack by all sorts of

No. 530] RELATIVE CONSPICUOUSNESS OF FOWLS 113

natural enemies. The total number of chickens involved

was 3,345. An account of the way in which the statistics

were obtained is necessary. All of these 3,343 chicks

were of known pedigree, and a numbered aluminum

leg band was attached to each one when it was re-

moved from the incubator in which it was hatched. A

record was made of each chick’s number. This num-

bered leg band was worn by the chick throughout its

life. Whenever a chick died a record of this fact was

made opposite its entry in the pedigree book. Dur-

ing the season every living chick on the range was

handled over twice and its leg band number checked back

with the original entry, and at the end of the season all

chicks remaining on the range were checked up.

Now it is clear that dead chicks which come to autopsy

will fall into two general classes: on the one hand, those

that died from one or another of the many diseases which

make the poultry raiser’s life a burden in the springtime,

and on the other hand, those killed by some enemy but not

carried away. In the latter class will fall the great ma-

jority killed by rats, some killed by skunks, and a fair

proportion of those killed by foxes. Usually a direct

record can be obtained for practically none of the chicks

killed by predaceous birds and cats. In 1909 we have

reason to believe that substantially all unrecorded deaths

were caused by predaceous birds.

At the end of the season when the birds are checked

up all will be accounted for as either (a) living, (b) dead

from some disease, (c) killed by recorded enemies, or

finally (d) missing. Of the missing birds there are two

classes again. On the one hand are those killed by ene-

mies which carried the carcases away, and on the other

hand, are those that through accident lost their leg bands,

and hence, while present in the flock, can not be entered

upon the records. With the methods of work in use here

the number of the latter class has always been small.

Unfortunately I am not able to give exact figures for such

birds for the season of 1909. It can be stated with cer-

114 THE AMERICAN NATURALIST [ Vou. XLV

tainty, however, that they did not exceed 25. Of this

number that lost their leg bands 8 were known to be self-

colored birds.

There were on the range in 1909 three classes of birds,

in respect to color pattern. These were (a) barred birds,

bearing either the pattern of the pure Barred Plymouth

Rock, or a modification of it;* (b) solid (self-colored)

black birds, resulting from the cross Cornish Indian

Game 3 X Barred Rock 2; and (c) pure Cornish Indian

Games of the dark variety which may for present pur-

poses be classed as self-colored birds.

With this somewhat lengthy explanation of the com-

position of the flock and method of keeping records in

hand we may proceed to examine the statistics of. elimi-

nation. In compiling these statistics the blank birds

which lost their bands (ca. 25) have been included with

the eliminated. This does not affect the conclusions in

any way because of the facts that (1) the number of such

birds is so small relatively, and (2) the proportion of

self-colored to barred birds among those which lost their

bands is relatively higher than in the general population

from which they came. The significance of this point

will be apparent as we proceed.

We have the following figures, it being understood that

‘eliminated’? means ‘‘killed by natural enemies’’ with

the inclusion of the small number of birds which lost their

bands as noted above.

Total number of birds = 3,343.

Number of barred birds = 3,007.

Number of self-colored birds = 336.

Total number of eliminated birds = 325.

Number of barred birds eliminated = 290.

Number of self-colored birds eliminated = 35.

The above figures include all eliminated birds, those

killed by recorded and unrecorded enemies together. If

we take only those killed by recorded enemies, which

*See Pearl, R., and Surface, F. M., ‘‘On the Inheritance of the Barred

Color Pattern in Poultry,’’ Arch. f. Entwicklungsmech., Bd. XXX, Fest-

Band fiir Roux), pp. 45-61, 1910.

No. 530] RELATIVE CONSPICUOUSNESS OF FOWLS 115

under the conditions prevailing on the plant in 1909

means practically those killed by rats, we have:

Number of barred birds eliminated by recorded ene-

mies — 68.

Number of self-colored birds eliminated by recorded

enemies = 6. .

From these figures the following proportions are de-

rived: Of the total number of birds 10.05 per cent. were

self-colored.

Of all the eliminated birds 10.77 per cent. were self-

colored.

If we consider by themselves the birds eliminated by

recorded enemies, we have:

Of the birds eliminated by recorded enemies 8.11 per

cent. were self-colored.

Putting the figures in another way we have:

Of the self-colored birds 10.42 per cent. were elimi-

nated by all enemies.

Of the barred birds 9.64 per cent. were eliminated by

all enemies.

Of the self-colored birds 1.79 per cent. were eliminated

by recorded enemies (chiefly rats).

Of the barred birds 2.26 per cent. were eliminated by

recorded enemies.

Of the self-colored birds 8.63 per cent. were eliminated

by unrecorded enemies (chiefly predaceous birds).

Of the barred birds 7.38 per cent. were eliminated by

unrecorded enemies (chiefly predaceous birds).

The conclusion to be drawn from these figures, which

involve a large number of individuals, is obvious. It is

that the relative inconspicuousness of the barred color

pattern afforded its possessors no great or striking pro-

tection against elimination by natural enemies, during the

season (April 1 to October 1) of 1909 on the poultry

range of the Maine Experimental Station. It might be

objected that if the eliminations by predaceous birds

alone could be separately recorded it would then be found

that against this class of enemies the barred pattern had

116 THE AMERICAN NATURALIST [Vou. XLV

great protective value, as suggested by Davenport’s fig-

ures. This, however, can hardly be the case in the pres-

ent statistics since if it be assumed that predaceous birds

killed relatively few barred chicks and relatively many

self-colored, then it must also be assumed that the other

unrecorded enemies showed a preference for barred

birds, since with all enemies taken together substantially

equal proportions of both kinds of birds were eliminated.

In other words, if we assume a selective elimination in the

case of predaceous birds, we are obliged to assume an

equal and opposite selective elimination on the part of

other unrecorded enemies. There is no evidence on which

such an assumption could be based.

These figures, of course, cover only one year’s expe-

rience, and are in no wise conclusive, but general obser-

vation indicates strongly that essentially the same re-

sult would be shown in other years if it were possible

to tabulate the figures. Unfortunately neither the

records of 1908 nor 1910 can be used for this purpose.

In 1908 there were almost no self-colored birds on the

range. In 1910, owing to the location of the houses

on the range and other circumstances which can not

be gone into in detail, thieves were active on the plant

and the birds taken were not a random sample of the

flock in respect to color. 1909 was a fortunate year

for such a study as the present one. The thieves con-

fined their attention to adult stock on a part of the plant |

away from the chicks, and left the latter strictly alone.

Definitely controlled observations regarding the elim-

ination of animals by natural enemies, covering a consid-

erable number of individuals and anything like a com-

plete range of enemies, are exceedingly scarce. The

whole question of the interplay of factors in the ‘‘strug-

gle for existence” constantly going on in the organic

world has been discussed very largely from the a priori

standpoint, throughout the whole period since the ap-

pearance of the ‘‘ Origin of Species.” The ‘‘rabbit with

his legs a little longer,’’ the ‘‘fox with the little keener

No.530] RELATIVE CONSPICUOUSNESS OF FOWLS ia

sense of smell,’’ the ‘‘bird of dull colors which har-

monized with the background,” et id genus omne, have

been made to do valiant service.

Ever since the first description, made by the Nurem-

berg miniature painter Rösel in 1746,° of a case of pre-

sumably protective coloration, we have been prone to

argue that because an organism was colored or formed in

such a way as to be inconspicuous it was, therefore, nec-

essarily protected from attack by its enemies to a greater

or less degree. The logic of such reasoning is flawless.

It ought to be protected. But a conclusion may be per-

fectly logical and still not true. In the study of pro-

tective coloration, including mimicry, it is essential that a

discovery that an organism is to human eyes inconspicu-

ous or not readily distinguishable from some other or-

ganism shall not be considered the final goal. Rather let

such a discovery always be supplemented by an experi-

mental or observational determination of whether this

inconspicuousness really helps the organism, in actual

practise, in avoiding elimination by natural enemies. It

is worth noting that more than one recent critical stu-

dent of these problems who has applied this method has

brought to light results essentially similar in their gen-

eral import to those set forth here.’

*Cf. Müller, H., ‘‘Schiitzende Aehnlichkeit einheimischer Insekten,’’

Senei, Jahrg. III, Heft 8, p. 114, 1879.

. for mmnte the chapter on ‘‘Colouration of Organisms’’ in Dewar

and Finn ’s ‘*The Making of Species’? (New York, seyi , and still more

recently the thorough critical study by Punnett on ‘‘ Mimicry in Ceylon

Butterflies, with a Suggestion as to the Nature of Polymorphism’? (Spolia

Zeylonica, Vol. VII, Part XXV, September, 1910, pp. 1-24, 2 plates).

SOME CONSIDERATIONS CONCERNING THE

PHOTOGENIC FUNCTION IN MARINE

ORGANISMS

F. ALEX. McDERMOTT

WASHINGTON, D. C.

In two very interesting papers, Professor C. C.

Nutting’ has brought forth evidence tending to show that

in oceanic depths below the range of penetration of the

sun’s rays, there exists a dim, phosphorescent light, quite

general in its distribution, radiated from various photo-

genic organisms of the abyssal regions, and having a defi-

nite and valuable significance for the life of animal forms

at these depths.

That such a light actually exists is scarcely to be sanely

doubted, in view of the evidence of the deep-sea explora-

tions which have added so much to the knowledge of

oceanic conditions. And that it has a purpose in the life

of the forms inhabiting those portions of the ocean beds

where it exists, seems to the writer equally undeniable,

unless we accept Emerson’s poetic reasoning that

“ Beauty is its own excuse for being.”

Just what its purpose may be in hermaphroditic, simple

forms not provided with definite organs of sight, and

indeed also in many higher forms, may, of course, still be

a legitimate subject for investigation and consideration.

Professor Nutting’s remarks have been of special

interest to the writer in connection with some recent

studies made by the latter on the general subject of bio-

photogenesis, with special reference to the: Lampyride.*

*(a) ‘*The Utility of Phosphorescence in Deep-sea Animals,’’ page

Nar., Vol. 3, 1899, pp. 792-799; (b) ‘‘The Theory of Abyssal Light,’’

Pros. VII Dano. Zool., advance reprint, 1910.

2 Amer. Journ. Physiol., 1910. Vol. 27, pp. 122-151; Canad. Entomol.,

1910, Vol. 42, pp. 357-363; Popular Sci. Monthly, 1910, Vol. 77, pp. 114-

121.

118

No. 530] THE PHOTOGENIC FUNCTION 119

The coloring and photogenicity of the organisms found

in the depths of the sea show some similarities to the

corresponding features of life on land.

Take the family Buprestide, of the genus Coleoptera,

of the order of insects. The insects of this family are

probably the most brilliantly colored of any of the beetles,

and are colored quite as brilliantly as the insects of any

other genus. The colors cover a quite wide range of

metallic, polished, glistening greens, blues, reds, coppery

and golden; many of the smaller species wear more

somber dark blues, browns and blacks, but as a class they

are brilliant and showy. Obviously, these colors would

be invisible in the absence of light, and need a light of

considerable intensity to bring out their full value. Now

we find that almost without exception these Coleoptera

are diurnal; they attain their maximum activity during

the brightest daylight, and fly but little at night. But one

species has been reported to be luminous, and unless this

report is pretty definitely confirmed there is grave reason

to doubt its authenticity.

Now let us consider the Lampyride: The beetles of this

family of almost eleven hundred species are in the great °

majority of instances, luminous; the non-luminous species

form a decided minority of the true Lampyride. They

are also, in the great majority of cases, mainly nocturnal

in habit, hiding out of the sunlight during the day; those

species which are markedly diurnal in habit are also those

which are non-luminous, or in which the luminosity is

relatively slight. In coloration, they show none of the

bright metallic, showy colors of the Buprestide; black,

gray, brown and yellow-brown predominate, with occa-

sional red markings, yellow stripes and indistinct lines

and spots. In them, the photogenic function possesses at

least two definite significances: (1) it is an adjunct of the

sexual organism of the insect, rendered of value to them

by reason of their nocturnal habits, and (2) it has a pro-

tective value. In the larve it might also be considered

to have an aggressive value, in attracting the snails. etc.,

120 THE AMERICAN NATURALIST [Vou. XLV

on which they feed, but this argument would not hold for

the imagos, which are much more active.

Most of the above statements apply with equal force

to the Pyrophorini, the luminous Elateride of the tropics;

these insects are herbivorous, however, and the aggres-

sive significance does not hold for them.

It would seem, then, very probable that similar condi-

tions obtain in the abyssal region, with its dim weird,

phosphorescent light. The light produced by the Lam-

pyride has recently been shown by Ives and Coblentz? to

have the extremely high radiant efficiency of 96.5 per

cent., against 4 per cent. for the best artificial illuminant.

The spectrum of this light is a continuous band extending

from the upper red to the lower blue with a maximum

intensity in the yellow-green. This spectrum is of wider

range than that of the sea-forms cited by Nutting,* but

can hardly be of less efficiency. The light of the Lam-

pyride is generally stated to be yellow, or greenish; there

are some slight variations among different species, but in

the main the lights are similar; it seems that a great many

of the marine organisms also give a light of similar

tone. Therefore colors whose wave-lengths are within

the limits of those of the emitted lights of these forms,

would be distinguishable in such a biophotogenic light.

Although we do not yet know the full details of the

process of the production of light by living forms, it is

not too much to assume that Nature has developed it to

a point very near to the maximum possible efficiency, and

if such is the case, the luminous oceanic forms could emit

a very penetrating illuminating radiation with very little

expenditure of energy, and though this light might not be

of any considerable intensity, as judged by our eyes, it

could undoubtedly serve as quite a useful light to the

large-eyed denizens of the deep.

The photogenicity of Salpa, Noctiluca and other such

simple forms, which are without definite organs of sight,

* Bulletin of the U. S. Bureau of Standards, 1910, Vol. 6, pp. 321-336.

t Supra b, page 10.

No. 530] THE PHOTOGENIC FUNCTION 121

presents other difficulties. It is not, however, necessary

to the faculty of perception of light that definite organs

should exist. It is a quite well-known fact that certain

worms, bacteria, and other low organisms are able to

detect ultra-violet rays to which the human organism is

wholly without sensible response, and yet these actino-

tropic (if a coined word may be pardoned) forms show

no definite organs such as might be adapted to the receiv-

ing and recording of the very short wave-lengths of ultra-

violet light. If, then, existing organisms are known to be

affected by ultra-violet rays for which they have no

special sense-organs, it is certainly logical to assume that

they and other forms may also be susceptible to the

longer and more easily discerned wave-lengths of visible

light—especially when those wave-lengths comprise

mainly the rays possessing the highest illuminating effect

—and without the necessity for the existence of ‘‘eyes’’

or other definite light-receiving organs. As a matter of

fact Noctiluca, and numerous other marine organisms

have been shown to be susceptible to light, although

they possess no specific organs for this function so far as

we have been able to make out.

Another consideration as to the purpose of the light

presents itself here. We must consider the nature of the

medium in which these creatures live. Water does not

lend itself as readily as does air to the diffusion of the

particles which produce the sensation of smell; and hence

while odors, or speaking more properly, from the stand-

point of marine organisms, flavors or tastes undoubtedly

exist in the ocean water, they could not, on account of the

water currents, lack of diffusion, etc., serve the purpose

which the odors of land animals serve of giving indication

of the presence and location of the creatures. It there-

fore would not be unreasonable to assume that in the gre-

garious simple luminous marine forms, the photogenic

function takes the place to some extent of the animal

odors of land forms.

To sum up, then:

122 THE AMERICAN NATURALIST [ Vou. XLV

From analogy to terrestrial forms, the photogenicity

and coloration of marine organisms must play some

essential part in their life histories;

The absence of definite organs for the reception of the

radiations of light may not necessarily indicate that the

forms from which they are absent are insensible to these

radiations;

' The photogenic function in certain simple marine

forms may replace the olfactory function of terrestrial

forms, to some extent.

SHORTER ARTICLES AND DISCUSSION

COMPUTING CORRELATION IN CASES WHERE SYM-

METRICAL TABLES ARE COMMONLY USED

In studying the assortative mating of Paramecium I have

found occasion to compute the correlation in many cases for

which double or symmetrical tables are commonly employed.

I have found that in such cases the use of symmetrical tables

is quite unnecessary and the computations can be performed

with much less labor without them. It will, therefore, be worth

while to show how the use of symmetrical tables can be avoided.

When the two objects to be compared are alike, as when the

two members, A and B, of conjugating pairs are examined,

evidently either A or B might be entered in either the horizontal

rows or the vertical columns of the correlation table. In such

cases, the mean computed from the rows, and that computed

from the columns are likely to differ, depending on which indi-

viduals were entered in the rows, which in the columns. If, for

example, the larger individual is always entered in the vertical

columns, the smaller in the horizontal rows, as in Table II, then

the means and standard deviations of the two sets will differ

much. As a result the coefficient of correlation computed in

the usual way will show varying values, depending on how the

pairs are entered in the table. From the collection shown in

Table II we can by varying the method of entering the pairs

get coefficients of correlation varying from 0.132 to 0.523.

Under such conditions Pearson (1901), Pearl (1907) and

others enter each pair twice, once in the rows, once in the col-

umns. This gives a ‘‘symmetrical’’ table, in which the sums

of either the rows or the columns include all the individuals.

This method is theoretically correct, since each individual func-

tions both as ‘‘principal’’? and as ‘‘mate’’; the coefficient of

correlation computed from such symmetrical tables is the cor-

rect one. But such symmetrical tables are cumbersome and

involve much labor. Pearl (1907) gives a formula by which the

same coefficient can be obtained without making symmetrical

tables, by computations involving the two means and standard

123

124 THE AMERICAN NATURALIST [ Vou. XLV

deviations and the coefficient of correlation found in the usual

way.

But it is possible to find the correct coefficient of correlation

from ordinary tables, and with much less labor than by either

the use of symmetrical tables or by the method given by Pearl.

To see how this can be done, it is well to examine a symmetrical

table prepared for computation of the coefficient of correlation,

such as is given in Table I. Here the large figures give the

frequencies, while the subscripts in smaller type give the prod-

ucts of the deviations from the approximate mean (37). There

are two main points to be considered: (1) How the quantity

30311323 3.4/3 5/3 63 (7/3 8/3 940/41 2143/4445

30 ; k$ 2

31 421 224 4

32 o 1

33 sel y. 32 12

34 2b Bg 2a 13} lf |13 2e |l2 12

35 ld | la 24® 3344|54 |36 23

36 le 13| 32 7 |3| 54 63 30

3 Ht 2-47 ane -

38 la 54 3:|7 22| 5a 5a] 6s| le 18440

39 544 |22| 2 26| 28| Ap 19

4 34 | 36] 6a d | 53| 26| Bq 24 214 la| 2h JBL

41 224120 Sal 2e) 2226 14

42| 135 25 J |65| 29 As lab 17

43 id iLp iL 3

44 lak 22 3

4 ls l

2 |4 |1 1212838033/4019 1114/117/3 |3|1 R50

TABLE I. SEET CORRELATION TABLE FOR THE ag OF 125 PAIRS

OF Paramecium au each individual orga ip twice, once in the vertical

columns, once in hes fad aces rows. (Unit of AE 4 microns.)

(xy) is to be correctly obtained; (2) how the mean and stan-

dard deviation are to be correctly obtained.

1. With regard to the first point, it will be observed that such

a table is divisible by a diagonal passing from the upper left-

hand corner to the lower right-hand corner into two halves which

are in all respects duplicates as regards both frequencies and

deviation products. (The frequencies through which the diag-

onal line passes are to be divided evenly between the two halves.)

It is evident, therefore, that if we use only one of these halves

No.530] SHORTER ARTICLES AND DISCUSSION 125

of the table in getting the sum S(wy) we shall get just one half

the sum we should get by using the whole table; the sum for the

whole table would therefore be obtained simply by doubling this

half-sum. Now, if in place of making a symmetrical table we

enter always the larger member of each pair in the vertical

columns, the smaller in the horizontal rows, we shall get a table

that is precisely one of these duplicate halves of the symmetrical

table; this will be seen by comparing Tables I and II. The

quantity (xy) from such a table will then be just half that

from the symmetrical table; it may then be doubled, and the

further computation will be identical with that for the symmet-

30, 31 32 33, 34 35, 86.37 38, 33, 40,41, 42,43, 44, 45,

A B C

30, ] L 2 2

31 1, 1, ar ie 4

$2, wp 1

33, 2,6 22| ls 32 Epa 21/12

34, 1, | 26 }15] 4 | Is Qs} | ded [9] 3422

35, 2, |3.|4 || |3 | fiq 6 2s

36, z 2:114 |3: | 52 | 63 we 23| 7 |30

38, 2, |22| 53| 54| 6s| 16| |1s{22/18 |40

39, Lel 2e | 20} Re | 7}a2}19

40, ls | 22] 215] ne] 2a] | 8/23 |31

41, he 1]13 |14

42, i {| p e | n?

43, ; g 3| 3

i x ETE 3| 3

a ee Ske es NEE

45, zis

8 23 6 7 ele 12231916 3 3 1J.

LE II. THE SAME TABLE SHOWN IN TABLE I, SAVE THAT EACH INDIVIDUAL

ENTERED BUT ONCE—the larger member of the pair in the vertical column, the

smaller in the horizontal row.

rical tables. Or (as we shall see) this half sum, which forms

the dividend in obtaining the coefficient of correlation, may be

divided by a number half as great as in the symmetrical tables,

giving the same result.

It will further be seen that if in place of entering all pairs in

the same way—the larger members in the columns, the smaller

in the rows—we enter some or all of them differently, this will

make no difference in the result. If in Table II, for example,

the pair showing measurements 44 by 34 were entered in the

reverse way, it would fall, no longer in the right upper quad-

126 THE AMERICAN NATURALIST [Vou. XLV

rant, but in the left lower quadrant, at the point marked X.

Here, as examination will show, it would receive the same sub-

script that it has now, and would count as negative, exactly as

it now does. Again, suppose the pair 36 by 31 were similarly

transposed ; it would still fall in the left upper quadrant, at the

point marked Y, where it would receive the same subscript as at

present and count as positive, just as at present. And so of all

other cases; the value of a pair is not altered in any way by

changes in the way it is entered in the table. In making the

table, therefore, the pairs may be entered only once and quite at

random, or in any way that is convenient.

2. With regard to the mean and standard deviation, the ap-

parent advantage of symmetrical tables is that they give us the

actual mean of all the individuals; it is to this mean that our

correlation must refer. But this actual mean ean readily be

obtained from the tables in which each pair is entered but once,

in any way that happens to be convenient. It is merely neces-

sary to add together the sums of the rows and of the columns

of the table. Thus in Table II the number of individuals having

the length 35 is not 17 (sum from the row beginning.with 35),

nor 6 (sum from the column headed 35), but 23 (sum from both

the row and the column) and so for all other classes. It will be

well to illustrate by an example certain of the steps in the com-

putation. Table II shows a correlation table of single entry, as

prepared for computation of the coefficients of correlation and

other constants.

After finding the sums of the rows (given in column A at the

right) and of the columns (given in B, underneath), we place

the latter sums (B) by the side of A, in the proper places (as

at B’), then add the two sets, giving the sums shown in the

column C at the right. These are the same sums that we should

get from a symmetrical table; adding these we get the total

number of individuals (250 in Table II). Now from this

column C we find the approximate mean in the usual way; it

lies in this case at the length 37 (with 38 individuals). Through

the column and the row headed 37 we therefore draw the lines

serving as axes of reference in finding the correlation- We now

find the correlation in the usual way. In so doing (1) we make

use always of the sums in the column C in finding mean, stan-

dard deviation, ete. (2) We use for both horizontal and ver-

tical axes of reference in computing the correlation in all cases

No.530] SHORTER ARTICLES AND DISCUSSION 17

a row and column with the same heading (37 in this case).

(3) We employ the ordinary frequencies in the body of the

table in getting the sum of the deviations of (xy) for use in the

formula for the coefficient of correlation, just as in ordinary cor-

relation tables. The computation of the coefficient is of course

(as in the case of symmetrical tables) considerably simpler

than in the usual case, since we have but one standard deviation

and one quantity d to deal with.

Only one other point in the computation is peculiar, requiring

careful observance. If we let n signify the number of pairs

and N the number of individuals (so that N = 2n), then in find-

ing the mean, standard deviation, and coefficient of variation,

we use N (just as in symmetrical tables), so that the formula for

the standard deviation is

= (OD a 0nk

But in getting the coefficient of correlation, the sum S(zy) :

which we get from our unsymmetrical table is just half what we

_ should get from a symmetrical table (as we have already seen).

Therefore, to make the computations identical with those for

symmetrical tables, we must either double this sum in the for-

mula for the coefficient of correlation, or what is simpler, in

place of doubling this sum we may halve the number by which

we divide this sum, that is, we may use n in place of N. us

the formula for the coefficient of correlation becomes by this

method

S 1

= (=e — «) x a

This method lends itself readily to the valuable procedure

recently described by Harris (1910) for finding the coefficient

of correlation, the only point requiring careful attention being

the fact that in finding the standard deviation we must use

N (number of individuals), while in the formula for the coeffi-

cient of correlation we must use n (number of pairs). The

present plan is likewise well adapted for finding the coefficient

of correlation by the ‘‘difference method’’ (see Harris, 1909).

If the method we have described is used, the pairs are entered

in the table but once, in any way that is convenient; the correla-

tion computed will always be the same, and identical with that

from symmetrical tables. It avoids the cumbersome and labo-

128 THE AMERICAN NATURALIST [ Von. XLV

rious symmetrical table; at the same time it involves much less

labor than the method given by Pearl. When there are many

tables to be computed, the amount of drudgery it saves is great.

PAPERS CITED

1909. Harris, J. A. A Short Method of Calculating the Coefficient of

Correlation i in the Case of Integral Variates, Biometrika, 7, 21

1910. Harris, J. A. The Arithmetic of the Product Moment Method of

Caleulating the Coefficient of Correlation. Amer. pate 44,

iS)

693-699.

1907. Pearl, R. A Biometrical Study of Conjugation in Paramecium.

Biometrika, 5, 213-297.

1901. Pearson, K. Mathematical Contributions to the Theory of Evolu-

iors. On the Principle of Homotyposis and its Relation to

Heredity, to the Variability of the Individual-and to that of the

Race. Philos. Trans., A, 197, 285-379.

THE JOHNS HOPKINS UNIVERSITY.

H. S. JENNINGS.

The Anatomical Laboratory

of Charles H. Ward

189 West Avenue, Rochester, N. Y.

= OUR HUMAN SKELETONS are selected specimens scientifically

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The American Naturalist

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Heredity

CONTENTS OF THE AUGUST NUMBER

: Chromosomes and Heredity. Professor T. H. MORGAN.,

3 Spiegler’s “White Melanin” ey oneness ae

: Recessive White. Dr. Ross AIKEN GoRTNER.

‘Shorter Articles and Correspondence: A

Š _ Contribution to Our Knowledge of Wasps:

Tia ak Tela Heredity, Dr, W. J. Serran.

. Pickwickian

Professor

CONTENTS OF THE SEPTEMBER NUMBER

Nuclear Phenomena of Sexual mopar in the

Dr, BRAD: Moore Dav:

Nuclear Phenomena of Sexual aera in Fungi,

PROFESSOR R. A. HARPER.

The Pose of the Sauropodous Dinosaurs. Dr, W. D.

MATTHEW.

Shorter Articles and Discussion : Evolution without Iso-

and Literature imal Structure and Habits,

AA G. H. PARKER, Plant Physiology, ©. L.

CONTENTS OF THE NOVEMBER NUMBER

eee of Skin Pigmenta tation in Man. Geamkues S

B. DAVENPORT.

MARCH, 1911

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AMERICAN NATURALIST

VoL. XLV March, 1911 No. 531

THE GENOTYPE CONCEPTION OF HEREDITY!

PROFESSOR W. JOHANNSEN

UNIVERSITY OF COPENHAGEN

Brotoey has evidently borrowed the terms ‘‘heredity”’

and ‘‘inheritance’’ from every-day language, in which the

meaning of these words is the ‘‘transmission’’ of money

or things, rights or duties—or even ideas and knowledge

—from one person to another or to some others: the

‘theirs’’ or ‘‘inheritors.’’

_ The transmission of properties—these may be things

owned or peculiar qualities—from parents to their

children, or from more or less remote ancestors to their

descendants, has been regarded as the essential point in

the discussion of heredity, in biology as in jurisprudence.

Here we have nothing to do with the latter; as to biology,

the students of this science have again and again tried to

conceive or ‘‘explain’’ the presumed transmission of

general or peculiar characters and qualities ‘‘inherited’’

from parents or more remote ancestors. The view of

natural inheritance as realized by an act of transmission,

viz., the transmission of the parent’s (or ancestor’s)

personal qualities to the progeny, is the most naive and

oldest conception of heredity. We find it clearly devel-

oped by Hippocrates, who suggested that the different

parts of the body may produce substances which join in

the sexual organs, where reproductive matter is formed.

* Address before the American Society of Naturalists, December, 1910.

129

130 THE AMERICAN NATURALIST [Vou. XLV

Darwin’s hypothesis of ‘‘pangenesis’’ is in this point

very consistent with the Hippocratic view, the personal

qualities of the parent or the ancestor in question being

the heritage.

Also the Lamarckian view as to the heredity of

“acquired characters’’ is in accordance with those old

conceptions. The current popular definition of heredity

as a certain degree of resemblance between parents and

offspring, or, generally speaking, between ancestors and

descendants, bears the stamp of the same conceptions,

and so do the modern ‘‘biometrical’’ definitions of hered-

ity, e. g., as ‘‘the degree of correlation between the

abmodality of parent and offspring.’’ In all these cases

we meet with the conception that the personal qualities of

any individual organism are the true heritable elements

or traits!

This may be characterized as the ‘‘transmission-con-

ception” of heredity or as the view of apparent heredity.

Only superficial instruction can be gained by working on

this basis. Certainly, medical and biological statisticians

have in modern times been able to make elaborate state--

patti of great interest for insurance purposes, for the

‘‘eugenics-movement’’ and so on. But no profound

insight into the biological problem of heredity can be

gained on this basis, for the transmission-conception of

heredity represents exactly the reverse of the real facts,

just as the famous Stahlian theory of ‘‘phlogiston’’ was

an expression diametrically opposite to the chemical

reality. The personal qualities of any individual organ-

ism do not at all cause the qualities of its offspring; but

the qualities of both ancestor and descendant are in quite

the same manner determined by the nature of the ‘‘sexual

substances’’—i. e., the gametes—from which they have

developed. Personal qualities are then the reactions of

the gametes joining to form a zygote; but the nature of

the gametes is not determined by the personal qualities

of the parents or ancestors in question. This is ued

modern view of heredity.

No. 531] GENOTYPE CONCEPTION OF HEREDITY 131

The main result of all true analytical experiments in

questions concerning genetics is the upsetting of the

transmission-conception of heredity, and the two differ-

ent ways of genetic research: pure line breeding as well

as hybridization after Mendel’s model, have in that

respect led to the same point of view, the ‘‘genotype-

conception’? as we may call the conception of heredity

just now sketched.

Here we can not trace the historical evolution of the

ideas concerning heredity, not even in the last ten years,

but it must be stated as a fact that a very great number of

the terms used by the modern biological writers have been

created under the auspices of the transmission-concep-

tion, and that perhaps the greater number of botanists

and zoologists are not yet emancipated from that old con-

ception. Even convinced Mendelians may occasionally

be caught using such words as ‘‘transmission’’ and other

now obsolete terms.

The science of genetics is in a transition period, becom-

ing an exact science just as the chemistry in the times of

Lavoisier, who made the balance an indispensable imple-

ment in chemical research.

The ‘‘genotype-conception,’? as I have called the

modern view of heredity, differs not only from the old

‘‘transmission-conception’’? as above mentioned, but it

differs also from the related hypothetical views of Galton,

Weismann and others, who with more or less effectiveness

tried to expel the transmission-idea, having thus the great

merit of breaking the ground for the setting in of more

unprejudiced inquiries. Galton, in his admirable little

paper of 1875, and Weismann, in his long series of fasci-

nating but dialectic publications, have suggested that the

elements responsible for inheritance (the elements of

Galton’s ‘‘stirp’? or of Weismann’s ‘‘Keimplasma’’)

involve the different organs or tissue-groups of the indi-

Vidual developing from the zygote in question. And

Weismann has furthermore built up an elaborate hypoth-

esis of heredity, suggesting that discrete particles of

132 THE AMERICAN NATURALIST [Vor. XLV

the chromosomes are ‘‘bearers’’ of special organizing

functions in the mechanism of ontogenesis, a chromatin-

particle in the nucleus of a gamete being in some way the

representative of an organ or a group of tissues.

These two ideas: that ‘‘elements’’ in the zygote corre-

spond to special organs, and that discrete particles of the

chromosomes are ‘‘bearers’’ of special parts of the whole

inheritance in question are neither corollaries of, nor

premises for, the stirp- or genotype-conception. Those

special ideas may have some interest as expressions of

the searching mind, but they have no support in experi-

ence; the first of them is evidently erroneous, the second

a purely speculative morphological view of heredity with-

out any suggestive value.

The genotype-conception of the present day, initiated

by Galton and Weismann, but now revised as an expres-

sion of the insight won by pure line breeding and Mendel-

ism, is in the least possible degree a speculative concep-

tion. Of all the Weismannian armory of notions and

categories it may use nothing. It is a well-established

fact that language is not only our servant, when we wish

to express—or even to conceal—our thoughts, but that it

may also be our master, overpowering us by means of the

notions attached to the current words. This fact is the

reason why it is desirable to create a new terminology in

all cases where new or revised conceptions are being

developed. Old terms are mostly compromised by their

_ application in antiquated or erroneous theories and

systems, from which they carry splinters of inadequate

ideas, not always harmless to the developing insight.

Therefore I have proposed the terms ‘‘gene’’ and

‘‘genotype’’ and some further terms, as ‘‘phenotype’’

and ‘‘biotype,’’ to be used in the science of genetics. The

‘‘gene’’ is nothing but a very applicable little word, easily

combined with others, and hence it may be useful as an

expression for the ‘‘unit-factors,’’ ‘‘elements”’ or ‘‘allelo-

morphs” in the gametes, demonstrated by modern

Mendelian researches. A ‘‘genotype’’ is the sum total of

No. 531] GENOTYPE CONCEPTION OF HEREDITY 133

all the ‘‘genes’’ in a gamete or in a zygote. When a

monohybrid is formed by cross fertilization, the ‘‘ geno-

type’’ of this F,-organism is heterozygotic in one single

point and the ‘‘genotypes’’ of the two ‘‘genodifferent”’

gametes in question differ in one single point from each

other.’

As to the nature of the ‘‘genes’’ it is as yet of no value

to propose any hypothesis; but that the notion ‘‘gene’’

covers a reality is evident from Mendelism. The Men-

delian workers have the great merit of being prudent in

their speculations. In full accordance with this restraint

—a quite natural reaction against the morphologico-

phantastical speculations of the Weismann school—it

may be emphatically recommended to use the adjectival

term ‘‘genotypical’’ instead of the noun ‘‘genotype.’’

We do not know a ‘‘genotype,’’ but we are able to demon-

strate ‘‘genotypical’’ differences or accordances. Used

in these derivated ways the term ‘‘gene’’ and ‘‘geno-

type’’ will prejudice nothing. The very appropriate

German term ‘‘Reaktionsnorm’’ used by Woltereck is, as

may be seen, nearly synonymous with ‘‘genotype,’’ in

so far as the ‘‘Reaktionsnorm’’ is the sum total of the

potentialities of the zygotes in question. That these

potentialities are partly separable (‘‘segregating’’ after

hybridization) is adequately expressed by the ‘‘geno-

type’’ as composed of ‘‘genes.’’? The ‘‘Reaktionsnorm”’

emphasizes the diversity and still the unity in the

behavior of the individual organism; certainly, the partic-

ular organism is a whole, and its multiple varying reac-

tions are determined by its ‘‘genotype”’ interfering with

the totality of all incident factors, may it be external or

internal. Thence the notion ‘‘Reaktionsnorm’’ is fully

compatible with the genotype-conception.

The genotypes can be examined only by the qualities

and reactions of the organisms in question. Supposing

*They may therefore be characterized as ‘*mono-genodifferent’’; this

term and the further terms ** di-genodifferent’’ and so on, may or may not

be of any use.

134 THE AMERICAN NATURALIST [ Vou. XLV

that some organisms of identical genotypical constitution

are developing under different external conditions, then

these differences will produce more or less differences as

to the personal qualities of the individual organisms. By

simple inspection of series of different individuals it will

be quite impossible to decide if they have or have not the

same genotypical constitution—even if we know them to

be homozygotic.2 We may easily find out that the organ-

isms in question resemble each other so much that they

belong to the same ‘‘type’’ (in the current sense of this

word), or we may in other cases state that they present

a disparity so considerable that two or more different

‘‘types’’ may be discerned.

All ‘‘types’’ of organisms, distinguishable by direct

inspection or only by finer methods of measuring or

description, may be characterized as ‘‘phenotypes.”’

Certainly phenotypes are real things; the appearing (not

only apparent) ‘‘types’’ or ‘‘sorts’’ of organisms are

again and again the objects for scientific research. All

typical phenomena in the organic world are eo ipso

phenotypical, and the description of the myriads of

phenotypes as to forms, structures, sizes, colors and other

characters of the living organisms has been the chief aim

of natural history, which was ever a science of essentially

morphological-deseriptive character.

Morphology, supported by the huge collections of the

museums, has of course operated with phenotypes in its

speculations concerning phylogenetic questions. The

idea of evolution by continuous transitions from one

‘*type’’ to another must have imposed itself upon zoolo-

gists and botanists, because the varying external condi-

tions of life are often‘ shifting the phenotypes in very

fine gradations; but also—and that is an important point

—because there may always be found considerable geno-

typical differences hidden in apparently homogeneous

populations, exhibiting only one single ‘‘type’’? around

* Here we are not concerned with the question of variable dominance, ete.

*Not always, as Bateson has the merit of having emphasized.

No. 531] GENOTYPE CONCEPTION OF HEREDITY 135

which the individuals fluctuate. For the descriptive-

morphological view the manifestations of the phenotypes

in different generations are the main point, and here the

transmission-conception immediately announces itself.

Hence we may adequately define this conception as a

“*phenotype-conception’’ in opposition to the genotype-

conception.

As already stated, the genotype-conception has been

gained in two ways: pure line breeding and hybridization.

The first way leads to an analysis of the existing stocks

or populations, the second way may realize an analysis of

the genotypical constitution of the individuals. The

analysis of populations has its most obvious importance in

all such cases, where the phenotypes are quantitatively

characterized. Even where individuals with consider-

able genotypical differences co-exist, the population may

—by simple inspection or by statistical appreciation—seem

to exhibit only one phenotype, this being usually charac-

terized by the average measure of the individuals (dimen-

sions, weight, intensity of any quality, number of organs

and so on). This is due to the fluctuating variability

swamping all limits between the different special pheno-

types in question (see the diagram).

Populations of self-fertilizing organisms (several

cereals and beans, peas and others) have offered the

Starting point for pure line breeding as a scientific

method of research. A pure line may be defined as the

descendants from one single homozygotie organism, ex-

clusively propagating by self-fertilization. ‘‘Pure line’’

is a merely genealogical term, indicating nothing as to

the qualities of the individuals in question. A ‘‘line’’

ceases to be ‘‘pure’’ when hybridization (or even inter-

crossing) disturbs the continuity of self-fertilization.

From a population of homozygotic self-fertilizers

there can be started (isolated) as many pure lines as

there are fertile individuals—of course very many of

such pure lines will be quite identical in genotypical

constitution and might in reality belong to one and the

136

THE AMERICAN NATURALIST

[Vot. XLV

REREN

ARAS

Nae E

EEEN

Ses

SA Sd

case the beans enclosed in glass-

l are

ostly impos-

e ne to which it

gs.—The fiu tions about the average length (

pure lines as well as in the mix

the phenotype) within the

ed population show no characteristic difference.

No. 531] GENOTYPE CONCEPTION OF HEREDITY 137

same pure line if the genealogy was but sure. The

guarantee of the descendence is thus a main point in the

principle of pure lines. Identity of genotypical nature

is not at all a proof for identical genealogy: the wide-

spread confusion of ‘‘resemblance’’ with ‘‘ genealogical

relation’’ is the root of much evil—of which the statis-

tics of biometricians have given us some instances.

The isolation of pure lines from plant-populations has

been the instrument for gaining the conviction that se-

lection is not able to shift the nature of genotypes.

The well-known displacement of the ‘‘type’’ of a popu-

lation by selection—this displacement proceeding from

generation to generation in the direction indicated by

the selection—is due to the existence a priori of geno-

typical differences in such populations (see the dia-

gram). By selection a relatively great number of those

organisms, whose genotypical constitution is favorable

for the realization of the desired degrees of any char-

acter, will be saved for reproduction; hence the result

of the selection!

Within pure lines—if no mutation or other disturb-

ances have been at work—or within a population in

which there is no genotypical difference as to the char-

acter in question, selection will have no hereditary influ-

ence. This result has in recent years also been reached

by several other experimenters in genetics. Here I also

may recall the brilliant experiments of H. S. Jennings

with Paramecium, experiments which have been carried

out quite independently of my own researches and which

have been of great importance for the propagation

and support of the genotype-conception. The bearing

It can not be detected by inspection that the five upper diagrams represent

Phenotypes which are genotypically pgp te while the nethermost diagram

—the sum of the others—indicates a phenotype masking five others. That

‘eae five phenotypes all are genotypically different is known a priori in this

Special case, but it could not be discerned by simple inspection.—In the popula-

tion genotypical pital are combined with merely individual fluctuations ;

within the single pure line only such fluctuations are seen. Hence, while selec-

tion within a pure line will have no hereditary op spate it is evident that any

Selection in the populenion must shift or move the “type” of the progeny in

the direction of selecti

138 THE AMERICAN NATURALIST [Vou. XLV

of these experiments has been attacked on the ground

that the Parameeciums multiply asexually; but this mat-

ter seems to me of no importance in the present case.

The experience that pure-line breeding of plants and

pure-strain cultures of micro-organisms, in full agree-

ment, demonstrate the non-adequacy of selection as a

genotype-shifting factor, is a circumstance of the great-

est interest. Also Woltereck’s experiments with

Daphnias, the important researches of Wolff, and the

highly interesting indications of C. O. Jensen as to

bacteria may be mentioned here as further supports for

this view. Quite recently Pearl has arrived at the same

conclusion as to the egg-production by fowls.

The famous Galtonian law of regression and its corol-

laries elaborated by Pearson pretended to have estab-

lished the laws of ‘‘ancestral influences’’ in mathemat-

ical terms. Now, by the pure-line explanation of the

well known action of selection in poly-genotypic popu-

lations, these laws of correlation have been put in their

right place; such interesting products of mathematical

genius may be social statistics in optima forma, but they

have nothing at all to do with genetics or general biol-

ogy! Their premises are inadequate for insight into the

nature of heredity.

Ancestral influence! As to heredity, it is a mystical

expression for a fiction. The ancestral influences are

the ‘‘ghosts’’ in genetics, but generally the belief in

ghosts is still powerful. In pure lines no influence of the

special ancestry can be traced; all series of progeny

keep the genotype unchanged through long generations.

A. D. Darbishire’s laborious investigations as to the

classical object of Mendel’s researches, green and yellow

peas, may even convince-a biometrician that the ances-

tral influence is zero in ‘‘alternative inheritance.’’ An-

cestral influence in heredity is, plainly speaking, a term

of the ‘‘transmission-conception’’ and nothing else.

The characters of ancestors as well as of descendants

are both in quite the same manner reactions of the geno-

No. 531] GENOTYPE CONCEPTION OF HEREDITY 139

typical constitution of the gametes in question. Partic-

ular resemblances between an ancestor and one or more

of his descendants depend—so far as heredity is re-

sponsible—on corresponding particular identities in the

genotypical constitution, and, as we have urged here,

perhaps to excess, the genotype is not a function of the

personal character of any ancestor.

The genotypic constitution of a gamete or a zygote

may be parallelized with a complicated chemico-phys-

ical structure. This reacts exclusively in consequence

of its realized state, but not in consequence of the

history of its creation. So it may be with the geno-

typical constitution of gametes and zygotes: its history

is without influence upon its reactions, which are de-

termined exclusively by its actual nature.

The genotype-conception is thus an ‘‘ahistoric’’ view

of the reactions of living beings—of course only as far

as true heredity is concerned. This view is an analog to

the chemical view, as already pointed out; chemical com-

pounds have no compromising ante-act, H,O is always

H,O, and reacts always in the same manner, whatsoever

may be the ‘‘history’’ of its formation or the earlier

states of its elements. I suggest that it is useful to

emphasize this ‘‘radical’’ ahistoric genotype-conception

of heredity in its strict antagonism to the transmission-

or phenotype-view.

As to the evolution of human civilization we meet with

true ancestral influences, viz., the tradition (comprising

literature, monuments of art, etc., and all forms of

teaching). Tradition is playing a very great réle, but

tradition is quite different from heredity. Nevertheless

there may often be danger of confusion, and here the use

of false analogs is not harmless. So an obscure meta-

phor is involved in archeologists’ reference to Greek

temples as ‘‘ancestors’? of some types of Christian

churches, or in their speaking of the descent of violins

from more primitive ‘‘ancestors.’’ Certainly, evolution

of types of tools, instruments and implements of all

kinds is—at least partially—going on by means of select-

140 THE AMERICAN NATURALIST [Vou. XLV

ive factors combined with tradition, the latter not only

conserving the valuable types but actively stimulating

their improvement. But all this has nothing at all to do

with the biological notion of heredity. It is of course

interesting to see that the idea of ‘‘evolution by selec-

tion” has won credit in archeology, sociology, etc., but

this involves nothing as to genetics, for which ‘‘tradi-

tion’’ is irrelevant.

The very ‘‘radical’’ form of the genotype-conception

advocated here may be too ‘‘theoretical’’ to be carried

through in all its consequences in cases of practical ex-

periments in genetics. In nature and even in the chem-

ical factories the chemical compounds are not always to

be had in quite pure state. The history of a prepara-

tion may sometimes be traced by accompanying impuri-

ties. As to the analogy with the genotypes we touch

here the question whether the genotypical constitution

of a gamete may not be accompanied by some accessorial

or accidental ‘‘impurities’’ from the individual organ-

ism in which the gamete was developed.

Here we meet with the cases of ‘‘spurious’’ heredity,

e. g., the infections of the gametes or zygotes as may be

seen in certain cases of tuberculosis, syphilis, ete. Such

and other forms of spurious heredity may have the ap-

pearance of ‘‘hereditary transmission’? or ‘‘ancestral

influence’’; but theoretically they do not interfere at all

with the genotype-conception of heredity. In such in-

teresting cases as that detected by Correns, viz., the

‘‘heredity’’ of a special form of albinism by ‘‘trans-

mission’’ through the plasm of the ovum—the sperm not

transmitting this character—we may at the first glance

be puzzled. Nevertheless, as Correns himself points out.

here we have certainly to do with a pathological state 0

the plasm or the chromatophores in question, and that

may perhaps be the reason for the lack of heredity

through the sperm which carries no (?) plasm or only a

small quantity. The etiology of such abnormalities

being as yet quite unknown, it may often be very difficult

to distinguish them clearly from ‘‘genotypically’’ de-

No. 531] GENOTYPE CONCEPTION OF HEREDITY 141

termined abnormalities which show the normal form of

heredity through both ovum and sperm. The case quoted

demands further experience and seems not to be in ac-

cord with results of Baur’s experiments. At any rate,

there may be several difficulties to overcome in the full

and consistent application of the genotype-conception,

difficulties that may be characterized as perturbations

by infection or contamination. And hereby it must be

r bered that theoretically, as well as practically,

there are no sharp limits between ‘‘normal’’ and ‘‘path-

ological’’ manifestations of life. ‘‘Nature is beautiful,

but not correct,’’ is a Danish saying.

The principle of pure lines or, generally, pure culture,

is of importance also for elucidating the celebrated ques-

tion of the inheritance of ‘‘acquired characters.” Men-

delism and pure-line researches are here in the most

beautiful accordance, both emphasizing the stability of

genotypical constitution; the former operating with the

constituent unities, the latter with the behavior of the

totality of the genotypes in question. The brilliant work

of Tower with Leptinotarsa and the highly suggestive

injection experiments of MacDougal indicate that

changes of the genotypical constitution are produced by

steps, discontinuously. And as yet no experiment with

genotypically homogeneous cultures has given any evi-

dence for the Lamarckian view, the most extreme

‘‘transmission’’-conception ever issued. As to bacteria,

the important experiments recently made by C. O. Jen-

sen for the purpose of changing their types through

adaptation have given not only absolutely negative re-

sults, but have demonstrated the fallacy of some posi-

tive indications by previous authors. Lamarckism and

selectionism are certainly at bottom the same thing: the

belief in personal qualities being ‘‘transmitted’’ to the

offspring. Observations in impure populations are now

their places of resort; nevertheless, it is granted that

their history in biology as suggestive ideas has been most

glorious. :

Apropos, some cases of apparent action of selection

142 THE AMERICAN NATURALIST [Vou. XLV

may have direct touch with Lamarckian ideas, as, e. g.,

De Vries’s selection of buttercups, recently quoted by

Jennings as ‘‘the only case that he has found’’ indi-

eating hereditary action of selection: ‘‘Here, after

selection the extreme was moved far beyond that before

selection.” And Jennings says: ‘‘Possibly repetition

with thorough analytical experimentation will show that

something besides selection has brought about the great

change. But at present the case stands sharply against

the generalizations from the pure line work.”’

Certainly Jennings is in reason, when he, on the

ground of his own masterly researches, looks out for

‘‘something besides selection.’’ There are three direc-

tions for the inquiry here. First, the strong evidence

that the buttercup-population was not at all homogene-

ous. Secondly, the possibility of intercrossing. I only

need to point out the beautiful researches of Shull as to

the effect of intercrossing in maize. The heterozygotes

were here larger and more productive than the pure

strains. The surprises of heterozygotic ‘‘constructions’”’

or of new combinations in F, may perhaps be respon-

sible for the case of De Vries’s buttercups; I shall not

try to discuss it. But, thirdly, we have an instance

pointed out several times by De Vries himself, viz., the

combination of selection with nourishment: ‘‘la sélection

c’est l’alimentation’’ as it has been said. I suppose that

we have here the essential point. The buttercups in cul-

ture have been better nourished than before the experi-

ments. Hence, the ‘‘best’’ genotypes having been se-

lected from the population and submitted to ‘‘better’’

nourishment, the result would easily be a moving of the

extremes far beyond those before selection. The butter-

cup-case seems to me to present no difficulties for the

genotype-conception.

The practical breeders are a somewhat difficult people

to discuss with. Their methods of selection combined

with special training and ‘‘nurture’’ in the widest sense

of this word are mostly unable to throw any light upon

questions of genetics, and yet they only too frequently

No. 531] GENOTYPE CONCEPTION OF HEREDITY 143

make hypotheses as to the nature of heredity and varia-

bility. Darwin has somewhat exaggerated the scientific

value of breeders’ testimonies, as if a breeder eo ipso

must be an expert in heredity. As to the principle of

pure lines it has been occasionally vindicated by Ger-

man authors, e. g., K. v. Riimker, that pure line breeding

is a thing old and well known. This is quite true; nearly

sixty years ago L. Vilmorin not only emphasized in a

lucid manner the importance of pure breeding, but he

even tried a little to use his experiences theoretically.

But it can not be denied that the principle of pure lines,

as a true scientific analytical implement, as an indispen-

sable method of research in heredity—not merely as a

questionable and, at any rate, unilateral and insufficient

method of practical breeding—is a novelty from recent

years. Had this analytical principle been used in the

times of Darwin, or had it even been appreciated in due

time by the biometric school, certainly the real bearing

of selection might long since have been rightly under-

stood also by the practical breeders of pure strains.

The genotypes may then be characterized as some-

thing fixed and may be, to a certain degree, parallelized

with the most complicated molecules of organie chem-

istry consisting of ‘‘nuclei’? with a multitude of ‘side-

chains.’’ Continuing for a moment such a metaphor, we

may even suggest that the genes may be looked upon as

analogs of the ‘‘radicals’’ or ‘‘side-chains.’’? All such

ideas may as yet be premature; but they are highly

favored by the recent researches of Miss Wheldale.

The fixity of a genotypical constitution in question is

the conception arrived at by Mendelian and pure line

work. Hence there is a discontinuity between different

genotypes. This discontinuity has been energetically

contested by several biologists, among whom Woltereck

may be pointed out as an important representative. In

his very interesting report on experiments with Daph-

mas, Woltereck indicates, as said above, that selection

was as yet ineffective; moreover he describes a case of

discontinuous alteration of type (mutation), and his ex-

144 THE AMERICAN NATURALIST [Vou. XLV

periments designed to confirm the Lamarckian view

have given as yet negative results, even though these

may be called ‘‘promising,’’ as he says. So all the evi-

dence of his breeding experiments is in reality quite in

favor of our genotype-conception !

But how much depends upon our mental eyesight,

what we see. Woltereck confesses openly his belief in

continuous evolution and remarks that for a convinced

selectionist of the Weismann school the new genotype-

conception is a ‘‘hard blow.’’ The aim of his paper in

question is to parry off such blows. Of course this parry

can not use his own statements just mentioned; as to

their obvious but inconvenient accordance with our con-

ception Woltereck might apply the famous words from

Harvey’s times: ‘‘video sed non credo.’’ Hence the

arguments must be taken from other observations, and

some very instructive results of cultures under varying

conditions have supplied the piéce de résistance for the

discussion. Woltereck is within his right when assert-

ing that we consider different genotypes as having con-

stant differences (like different formulas in chemistry).

This is an essential point; but Woltereck, admitting no

constancy in the differences, tries to demonstrate that

our view must be fallacious.

In a very suggestive manner he presents ‘‘phenotype-

curves’’ for several pure strains. These curves are

graphical schemes expressing (for the strain in ques-

tion) the average degree or intensity of any particular

character as it manifests itself under different condi-

tions, e. g., the relative length of heads by poor, inter-

mediate and rich feeding, ete. Such ‘‘phenotype-

curves’? may indeed be very useful as records of the

behavior of the organisms in question, and they mark

certainly a valuable progress in descriptive methods.

The phenotype-curves of the Daphnias in question

sometimes show rather constant differences between the

pure strains compared; but mostly this is not the case.

Especially under extreme conditions, e. g., with poor oT

even with very rich feeding, some of the curves are con-

No. 531] GENOTYPE CONCEPTION OF HEREDITY 145

fluent. So the differences between the phenotype-curves

may vary considerably or may even vanish entirely.

These experiences agree with numerous observations of

Wesenberg Lund as to the Daphnias in the Danish lakes,

and there is no doubt as to their correctness.

But when Woltereck thinks that these facts are in-

consistent with the existence of constant differences be-

tween the genotypes, he shows himself to have totally

misunderstood the question! Of course the phenotypes

of the special characters, i. e., the reactions of the geno-

typical constituents, may under different conditions ex-

hibit all possible forms of transition or transgression

—this has nothing at all to do with constancy or incon-

stancy of genotypical differences.

Every student of genetics ought to know this; some

few examples may suffice to enforce it: Temperature has

great influence upon the intensity of color in flowers; all

shades of intensity from saturated reddish-blue to pure

white may be observed with different temperatures in

lilac flowers of the ‘‘colored’’ varieties. Such pure

white flowering individuals are—as to color—pheno-

typically not distinguishable from genotypically pure

‘white? varieties. Nobody will assume that there

should be genotypical transitions here! Pure lines of

beans may in one year be different in size, e. g., the

average of the line A exceeding that of B. In another

year B may exceed A, or their average sizes may be

practically identical. Differences of soil may produce

something similar, and it is well known to breeders that

Some strains of wheat yield relatively much better than

others on rich soil, while the reverse is realized on

poorer soils. In four subsequent years two pure lines of

barley, both characterized by a considerable degree of

disposition to produce vacant spikelets (aborted grains)

in the heads, presented the phenotypes here indicated in

percentages of such vacancies.

Pure line L: 30 33 27 29

Pure line G: 5 45 3 28

146 THE AMERICAN NATURALIST [Vou. XLV

The genotype-differences are nevertheless constant;

the ‘‘Reaktionsnorms’’ of the organisms in Woltereck’s

cases, as well as in the examples just cited, are of course

eo ipso ‘‘constantly different’’ just as well as the ‘‘ Reak-

tionsnorms’’ of different chemical compounds. And as

to chemical analogies it may perhaps be useful to state

that different chemical compounds (the structural or

constitutional differences of which surely are granted to

be discontinuous and constant) may sometimes show

‘‘reaction-curves’’ highly resembling Woltereck’s ‘‘ phen-

otype-curves.’’ It is, I suppose, quite sufficient to point

out the temperature-curves of solubility for different

salts of sodium and other metals. These curves inter-

fere in different ways, cutting each other or partially

confluent, in analogy with Woltereck’s phenotype-curves.

The essential point in the whole matter is, of course,

that a special genotypical constitution always reacts in

the same manner under identical conditions—as all

chemical or physical structures must do. Differences in

genotypical constitution (as well as differences in chem-

ical or physical nature) are not bound to manifest them-

selves at all—and still less to do so in the same sense

—under all conditions. Sometimes even quite special

conditions may be required for the realization of possi-

bilities (‘‘Potenzen,’’ as some German authors are say-

ing), due to a special genotypical nature: This is a well-

known fact in physiology as in the fine art of gardening.

Baur has long since emphasized the importance of this

point for the Mendelian researches.

So the criticisms of Woltereck as to the genotypical

discontinuity and constancy are only based upon a re-

grettable misconception of the genotype-notion. Over

and over we find in current literature this confusion of

genotypes with phenotypes, and we even have met with

the idea, that the Daphnias of a lake may in summer

diverge in different races or varieties, but that in winter

they converge into one single race! In this statement of

Wesenberg Lund, the author regards of course only the

phenotypes in a purely descriptive manner. It is evident

No. 531] GENOTYPE CONCEPTION OF HEREDITY 147

that Woltereck’s view has been influenced by Wesenberg

Lund in this matter; but what might be fairly excused in

the latter is not allowable for an experimenter pretending

to work with cardinal questions of genetics.

Discontinuity and constant differences between the

‘‘oenes’’ are the quotidian bread of Mendelism, and here

the harmony of Mendelism and pure line work is perfect.

We have dealt with some recent criticism of the pure line

results; now it is time to look at Mendelism. The aston-

ishing evolution of this mode of research has given an

almost interminable stock of special results, and cases

that at first might seem incompatible with the Mendel-

ian views have been analyzed more thoroughly on a

large scale and have shown themselves quite in accord-

ance with Mendelism. The magnificent book of Bateson

gives a full account of this prosperous state of Mendel-

ian research. And it may be evident that Mendelism

gives the most striking verification of the essential point

in Galton’s ‘‘stirp-hypothesis’’: the inadequacy of

the personal quality in heredity. At the same time it

overthrows totally the idea of ‘‘organs’’ as being repre-

sented by the unities of the ‘‘stirp,’’ pointing out that

the personal qualities of the organism in toto are the re-

sults of the reactions of the genotypical constitution.

The segregation of one sort of ‘‘gene’’ may have influ-

ence upon the whole organization. Hence the talk of

‘“‘genes for any particular character’? ought to be

omitted, even in cases where no danger of confusion

Seems to exist. So, as to the classical cases of peas, it is

not correct to speak of the gene—or genes—for ‘‘yellow’’

in the cotyledons or for their ‘‘wrinkles,’’—yellow color

and wrinkled shape being only reactions of factors that

may have many other effects in the pea-plants. It

Should be a principle of Mendelian workers to minimize

the number of different genes as much as possible.

Here we meet with the questions of correlation and

‘coupling’? of genes. I can not here enter into a discus-

Sion as to the notion of ‘‘correlation’’ with its several

meanings; in my ‘‘Elemente der exakten Erblichkeits-

148 THE AMERICAN NATURALIST [Von XLV

lehre’’ a rather full discussion is to be found. I may only

point out here that many cases of presumed correlation

may simply be cases of two or more characters (reac-

_ tions) due to the presence—or even absence—of one

single gene. The phenotypically distinct and even di-

versely localized ‘‘characters’’ convey easily the impres-

sion that they are reactions of different genes.

The highly interesting experiences of Correns, Don-

caster, Morgan, Spillman and others as to the sex-de-

termining factors, are in some way connected with

researches of correlation and ‘‘coupling’’ of genes. The

discussion of the ingenious Bateson-Punnett scheme for

Abraxas and Morgan’s suggestive schemes as to Droso-

phila may favor the idea of what may be called ‘‘rami-

fied’’ genes. Castle has in his splendid researches as to

color-factors in rabbits, ete., initiated a systematic de-

scription of the (partially) analyzed genotypes, some-

what resembling the formulas of organic ‘‘structural

chemistry.” If we suggest an analogy between the

radicals of chemistry and the genes, the (partial) geno-

type-formulas in Castle’s manner may be able to demon-

strate ramifications of the genes inserted upon the main

group of the genotype-constituents. Pausing a moment

on this metaphor, it may be suggested that the ‘‘branch.”’

or ‘‘branches’’ of a ramified gene may be more difficult

to separate from its ‘‘trunk’’ than the whole gene from

the totality of the genotype. I shall here only ask if such

views may be of any use as working hypotheses. Their

bearing as to the realization of mutations is obvious,—

but the purely speculative nature of these suggestions

can not as yet warrant a longer discussion here.

It should always be borne in mind that the Mendelian

analysis is purely relative. Baur and Shull and even

several others have emphasized this fact when discussing

the segregations in their experiments, and Shull has

clearly pointed out that it may be quite impossible to in-

dicate whether a particular reaction (character) is due

to something positive or to the lack of a factor in the

genotypical constitution. All that can as yet be deter-

No. 531] GENOTYPE CONCEPTION OF HEREDITY 149

mined in this regard by Mendelian analysis is the nwmber

of differing points between the two gametes forming a

heterozygote. Such differences may be termed ‘‘geno-

differences.’’ The well-known facts, that a ‘‘character’’

may be dominant in some hybrids but recessive in others,

and that segregation in different cases may be very dif-

ferent, indicate that ‘‘characters’’ are complicated reac-

tions. The famous case of Bateson’s fowl-hybrids as to

the form of comb may here be quoted as an example: In

Walnut comb X Rose comb the latter is recessive, in’

Single comb X Rose comb it is dominant, and in both

casesthe segregation gives three dominants : one recessive.

Now Bateson has shown that ‘‘Walnut’’ is a compound

of Rose- and Pea-comb. Homozygotic Walnut differs

from homozygotie Rose only in one point, as does Rose

compared with Single. But Walnut-gametes differ from

Single-gametes in two points; hence Walnut X Single,

with Walnut as dominant, segregates in Walnut, Rose,

Pea and Single in the proportions 9:3:3:1. Even with

this analysis it is as yet not possible to decide whether

Single or Walnut is the form of comb for the realization

of which the greater number of positive factors are re-

quired. Suggesting—what seems to be the most prob-

able assumption—that Walnut is the most geno-compli-

cated case, Single may even be an expression for a

multitude of genes in the fowl-constitution. The rela-

tivity of the analysis by segregation must in all such

cases be remembered, and it is quite erroneous to think

that dominance indicates the positivity of the ‘‘unit-

factor’’ in question: So ‘‘Horns’’ are in Wood’s cases

dominant in male sheep but recessive in female sheep.

And as to analogs with chemical reactions it must be

kept in mind that a characteristic reaction may be the

consequence of lack of any substance as well as de-

pendent upon the presence of any special compound in

the solution in question.

The elaborate work of Mendelians of recent years has

shown very complicated segregations, and the most spe-

cialized segregation is almost the most specialized analy- —

150 THE AMERICAN NATURALIST [Vou. XLV

sis still known of any ‘‘character’’ in question. The

‘‘units’’ or ‘‘unit-factors’’ stated in Mendelian work are

consequently quite provisory, depending essentially upon

the number of genodifferences in the special crossing.

Probably it may be discovered that several such ‘‘unit-

factors’’ for one character may also be elements for the

realization of quite other characters. If this be the truth,

then the present state of Mendelism, characterized by

the rapidly augmenting number of new ‘‘unit-factors’”’

demonstrated in the organization of different biotypes

able to hybridize, may be replaced by a period in which `

many such unit-factors will be identified. At any rate

there is no reason to believe that the further Mendelian

analysis will augment the number of genes into absurd-

ity. The enormously increasing possibilities of combina-

tions by augmentation of the number of segregable genes

are a source of interest also in this connection.

As to cases of hybridization, in which segregation and

combination do not suit the Mendelian ‘‘laws,’’ it must

at first be stated that some apparent exceptions are prob-

ably caused by non-homogeneity of the initial material

for experiments. The experiments of Correns, Castle,

Miss Saunders, Tschermak and others have shown to

excess that phenotypes may seem totally ‘‘pure’’ and

nevertheless be heterogeneous (e. g., white flowering

stocks or albino mice). Thus constancy as to the pheno-

type of the progeny is no sure proof for genotypical

purity or unity. In discussing alternative inheritance

we meet with difficulties of the same nature as in regard-

ing fluctuating variability: the inadequacy of pheno-

type-description as the starting-point for genetic in-

quiries.

Secondly, the more or less high vitality of the different

combinations of genes in F, may perturb the Mendelian

results, as Baur has illustrated; in other cases the dif-

ferent degree of facility with which the union of special

gametes is realized may influence the relative numbers

of representatives in the F,-generation, as Correns has

demonstrated.

No. 531] GENOTYPE CONCEPTION OF HEREDITY 151

Here we can not discuss the difficulties in a complete

carrying through of the Mendelian analysis; Bateson’s

recent book contains a richness of instances concerning

this matter. Only one instance of special importance

may be mentioned here, viz., the so-called ‘‘ blended in-

heritance’’ opposed to Mendelian segregation or ‘‘alter-

native inheritance.’’ In cases of blended inheritance the

genes in question might be supposed to ‘‘fuse together’’

by the act of hybridization, or, in accordance with the

presence- and absence-view, the gene unilaterally carried

to the zygote might here in some manner be ‘‘diluted.’’

In this way, which certainly is very badly compatible with

the conception of genes as unit-factors, failing segrega-

tion might be explained.

Cases of failing segregation seemed to be abundant in

the beginning of the modern Mendelian era; Mendel him-

self pointed out some typical cases in the species-hybrids

of Hieracium. And Correns’s indication as to the con-

stant intermediate stature of maize stems seemed to be

a crucial case. Now the insight won by breeding experi-

ments as well as by cytological researches concerning

the phenomena of apogamy has put the question in a new

light. The discoveries of Murbeck, Raunkier, Ostenfeld,

Rosenberg and others have led to quite other explana-

tions as to the constancy of several intermediate hybrid

forms. In such cases no segregation is realized, because

no gametogenesis is going on—and in such cases there is

no reason for supposing any ‘‘fusing’’ or ‘‘dilution’’ of

genes. And as to Correns’s experiments, this careful

author has himself withdrawn the suggestion in question.

But still cases of ‘‘blending inheritance’’ remain.

Among these Castle’s experiences as to the dimensions of

rabbits, especially the length of ears, are the most impor-

tant and most discussed instances. Castle has in a con-

vincing and suggestive manner demonstrated that the

complicated color-characters in rabbits agree with the

Mendelian laws. Therefore much stress might be laid

upon his indication of cases contrary to these laws.

152 THE AMERICAN NATURALIST [Vou XLV

Crossing short-eared and long-eared races, he gained

an F’,-generation with almost intermediate ears, and here

no segregation was observed in F,.

But even this case may agree with Mendelian laws.

The idea for such interpreting is won—as Lang has

clearly pointed out—by means of Nilsson-Ehle’s (and

_ East’s) experiments, the former concerning the colors of

wheat-grains, the latter dealing with the number of

‘‘rows’’ in the ears of maize. Nilsson-Ehle demonstrated

that blending of red and white color in wheat is appa-

rently a fiction: The red color is determined by several

different genes, acting in the same sense and augmenting

the effect of each other. Hence by segregation and new

combinations of these approximately equipotent genes a

whole series of gradations in red color will be realized.

And these gradations must group themselves symmet-

rically around the phenotype of the F, in question. If

_we have to consider say three genes, A, B and C, we shall

for F, use the formula AaBbCe, indicating the value 3

which is intermediate between aabbee as zero and

AABBCC as 6. Even in case of no fluctuation such a

series must present itself as an almost continuous grada-

tion, and it is not difficult to find out that the progeny of

every ‘‘class’’ here will breed true, i. e., the average of

the progeny’s character will be like the ‘‘class’’ of the

parent.

Just so it is in the case of Hast’s experiments with

maize, as East himself has clearly illustrated. Thus,

well-analyzed instances of heredity in plants, concerning

both color-factors and meristic factors may be compared

with Castle’s case in question. Lang in his interesting

criticisms points out that certain irregularities in Castle’s

F,-material give strong evidence for the view that we

have no blended inheritance but true segregation here as

well as in the cases of Nilsson-Ehle (and, as we may add,

in the cases of East). Further analysis may then prob-

ably demonstrate in a more direct manner the true nature

of the apparent blending in Castle’s case; as yet we can

No. 531] GENOTYPE CONCEPTION OF HEREDITY 153

only say that this case does not seem incompatible with

Mendelian views. It must also be borne in mind that

certainly there have been very many genodifferences

between the differing races intercrossed in Castle’s

experiments. Hence these experiments are really operat-

ing with highly poly-heterozygotic F,-generations. And

how great influence upon dimensions (of ears and other

parts of the body) those color-determining genes may

have exercised can not be easily determined.

As to beans, it is proved that genes, effective in color-

reactions, may also have great influence upon the dimen-

sions and forms. So in my crosses a special factor,

which makes yellow color turn into brown and causes

violet to be turned into black, has a very marked influence

upon the size and form of the beans in question. Here

exact data are not necessary; the instance exemplifies the

two incident matters of fact, viz., that apparently simple

‘‘dimensional’’ or meristic characters may be determined

by several different genes, and that one sort of gene may

have influence upon several different reactions.

Then it seems that Mendelian analysis is proceeding in

a very prosperous way; but there may be even very

narrow limits for this analysis: the entire organization

may never be ‘‘segregated’’ into genes! But still there

is much to do in carrying through the genotype-concep-

tion as far as possible.

As to cytological researches the genotype-conception is

as yet rather indifferent. Certainly the process of segre-

gation must be a cell-action intimately connected with

division. But all the innumerably detailed results of the

refined cytological methods of to-day do not elucidate

anything as to segregation. It seems to the unprejudiced

observer that the much-discussed cytological phenomena

of karyokinesis, synapsis, reduction and so on may be

regarded rather as consequences or manifestations of the

divisions, repartitions and segregations of genotypical

constituents (and all other things in the cell) than as

their causes. This view is applicable even in those cases

154 THE AMERICAN NATURALIST [Vou. XLV

where sex-determination can be diagnosticated cyto-

logically.

In the discussion as to the existence of true graft-

hybrids the cytological configurations have of course a

high importance as precisely defined characters of cells

in such cases where the cytological elements of the two

species in question are different. And, as it may be well

known, cytological evidence is not at all favorable for the

idea of graft-hybrids. But the use of cytological configu-

rations for diagnosis is quite different from the idea that

special cytological elements might have importance for

the phenomena of heredity.

The question of chromosomes as the presumed ‘‘ bearers

of hereditary qualities’’ seems to be an idle one. I am

not able to see any reason for localizing ‘‘the factors of

heredity” (i. e., the genotypical constitution) in the

nuclei. The organism is in its totality penetrated and

stamped by its genotype-constitution. All living parts of

the individual are potentially equivalent as to genotype-

constitution. In botany there has been no doubt as to

this conception, and as to animals, O. Hertwig has for a

long time advocated the same view against the views of

Weismann and others, who have suggested that ontogene-

sis is partly determined or at any rate accompanied by a

progressive simplification of the ‘‘anlagen’’ (as we say

the ‘‘genotype-constitution’’) in the cells of the growing

embryo. The agencies of normally varying ambient con-

ditions and the interactions of specialized parts in the

developing individual may exercise their strong influence

upon the whole phenotypical state of the resulting partic-

ular individual. But these factors will as a rule not

change or shift the fundamental genotypical constitution

of the biotype in question. Later on we shall touch the

problem of such genotypical changes (the mutations)

induced by external factors.

Here we have to point out the fact that ‘‘living

matter’’—or, with a more precise definition, those sub-

stances or structures the reactions of which we call oe

No. 531] GENOTYPE CONCEPTION OF HEREDITY 155

‘‘manifestations of life,’’—is inter alia characterized by

the property of autocatalysis. The autocatalysis of

living beings must embrace the totality of their geno-

typical constituents. It seems to me that this autoca-

talysis as well as the compensative and complemental

maintenance of genotypical equilibrium in the organisms,

present some of the greatest enigmas of organic life.

The discussion of cytological problems leads us to the

question of pure or impure segregation. In the begin-

ning of modern Mendelian researches several instances of

presumed impure segregation of genes in gametogenesis

were discussed, e. g., as to color factors in animals. But

more thorough analytical experiments have in many such

cases demonstrated ‘‘purity’’ in the gametes, the charac-

ters in question having proved to be more complicated

reactions than at first supposed. Recently Morgan has

discussed the question in a quite new manner, suggesting

—as a working hypothesis—that the segregation might be

not of qualitative but of merely quantitative nature.

Hence the gametes should as a rule not be pure. Never-

theless, as the author illustrates by means of interesting

diagrams, the F,-generation of a monohybrid with normal

dominance might be composed of two classes of indi-

viduals sharply defined. And the author suggests that

this idea might be able to explain ‘‘the graded series of

forms so often met with in experience and so often

ignored or roughly classified by Mendelian workers.’’

Here we again touch the question of ‘‘blended in-

heritance.” I suppose that the above-mentioned expla-

nations by Lang and East are more consistent with the

real nature of the graded series in question. Now the

Mendelian work has not only been able to demonstrate

that several cases of segregation apparently impure are

pure segregations of complicated nature; but even the

““spotted conditions’? as to color in animals and plants,

emphasized by Morgan as a puzzling case, does not seem

to present any real difficulty for Mendelian explanation.

Certainly such cases as Shull has pointed out, viz., hetero-

156 THE AMERICAN NATURALIST [Vou. XLV

zygotic nature being necessary for ‘‘mottling’’ in some

special bean-hybrids, may at first glance favor the idea of

‘‘snotted conditions’’ being due to irregular segregation

or to different repartition of color-determining factors in

the tissues in question. But a closer examination seems

to vindicate the real existence of special ‘‘spotting

factors.’’ The very interesting researches of Lock as to

the ‘‘Inheritance of certain invisible characters. in peas’’

have clearly pointed out a ‘‘spotting’’ factor or a

‘‘pattern’’-determiner in peas, independent of any color-

manifestation. It must be borne in mind that a multitude

of characteristic epidermal ‘‘patterns’’ are found in

animals and plants, these patterns concerning all epider-

mal manifestations and often showing a widely fluctuat-

ing variability. As to the realization of all such spots it

might be suggested that in neighboring parts of the devel-

oping epidermal tissue some little difference of ambient

conditions may inhibit or even release reactions, the alter-

nation of which produces the spots.

The whole case seems to be somewhat analogous to the

merely phenotypical phenomena of alternative variability

first pointed out by De Vries, e. g., the alternation of

decussated and contorted stems of Dipsacus. Here we

touch the highly suggestive idea of ‘‘ sensible periods’’ in

ontogenesis or histogenesis emphasized with so good

experimental arguments by De Vries. Of course there

must be a genotypical fundament for the existence of the

alternating character in question, e. g., for the particular

nature of the surface of the spots (or for the contortion

in Dipsacus, ete.); strains without such genotypical

fundament will not be spotted (nor produce contorted

individuals at all)—These remarks are made only to

point out that Morgan may have exaggerated a little his

criticisms as to ‘‘spotting factors,” but I confess that this

question is in need of closer analysis. :

Then the problem of pure or impure segregation may

still be open; but the tendency in modern genetics goes

certainly in the direction of establishing pure segrega-

No. 531] THE GENOTYPE HYPOTHESIS 157

tion as the normal case. If we accept the suggestion of

autocatalysis as an essential factor for the propagation of

living matter in general, and hence eo ipso, for the growth

or multiplication of genotypical constituents, we might in

case of impure segregation expect frequently to find

‘‘dominants’’ in the progeny of ‘‘recessives’’; and the

numerical proportions of the dominants and recessives in

consecutive generations must be rather irregular. But

this is not the case. The recent experiments of Darbi-

shire quoted above demonstrate in a beautiful manner the

purity of segregation during subsequent generations in

Mendel’s classical object, the pea.

Francis Bacon says: ‘‘Human understanding easily

supposes a greater degree of order and equality in things

than it really finds.’? So we may in modern genetics be

aware of the relativity and narrowness of our provisorial

explanations, remembering Bacon’s warning that ‘‘many

things in nature may be sui generis and irregular!’

Among the irregularities in heredity we may reckon the

mutations, observed in nature as well as in more precisely

defined conditions of artificial experiments. From the

famous observations of De Vries and the indications of

several earlier authors, to the modern experimental

researches of MacDougal, Standfuss, Tower, Blaringhem

and others, all evidences as to mutations point out the

discontinuity of the changes in question. Here we need

not enter the question; it is sufficient to state that the es-

sential point is the alteration, loss or gain of constituents

of the genotype. The splendid experiments of Tower as to

Leptinotarsa have in the most evident manner shown that

the factors which produce the mutations in this case, viz.,

the temperature and state of moisture, are able to act in

a direct manner upon the genotypical constitution of the

gametes; and Tower has noted the occurrence of Mendel-

lan segregation in hybridizing his mutants with the

original unaltered biotypes. There may in some cases

be certain puzzling irregularities to be explained by

future researches, but it is evident that in all such muta-

158 THE AMERICAN NATURALIST [Vou. XLV

tions, discontinuity is the characteristic feature in the

change of type.

As to populations, the biotypes of which may practi-

eally exhibit continuous transitions—like the case of my

own populations of beans—the idea might be born that

biotypes are evolved from each other by extremely small

steps in genotypical change. Hence such mutations must

be practically identical with ‘‘continuous’’ evolution.

But there is no evidence for this view. Certainly in such

populations the ‘‘static’’ transitions between the geno-

typical differences manifesting themselves. in several

characters may be called continuous—but such a ‘‘con-

tinuity of museums,’’ as it might be called, is not at all

identical with genetic continuity. Galton himself has

emphasized the capital difference between the notions of

continuity in collections and continuity in origin, and as

yet the mutations really observed in nature have all

shown themselves as considerable, discontinuous salta-

tions. So in my own still unpublished experiments with

pure lines. Natura facit saltus. The chemical analog

to such mutations may be the formation of homologous

alcohols, acids and so on. The greater mutations may be

symbolized by more complicated molecular alterations.

But such analogs are of very little value for the under-

standing of genetic evolution.

The genotype-conception supported by the great stock

of experiments as to pure line work, Mendelism and muta-

tions does not consider personal adaptation as a factor of

any genetic importance. Phrases as ‘‘cl ters, won by

adaptation and having successively been hereditarily

fixed,” are without meaning from our point of view.

Hence much talk of adaptive characters successively

gained seems to us an idle matter. A closer study of

desert-organisms and the like may elucidate such things;

here the suggestive researches of Lloyd as to stomates in

desert plants may be pointed out. And as to the old

question of ‘‘mimiery,’’ this problem in the famous cases

of butterflies has in a most convincing manner been put

No. 531] GENOTYPE CONCEPTION OF HEREDITY 159

into Mendelian terms by the observations and experi-

ments of Punnett, de Meijere and others. This strong-

hold of the united Lamarckism and selectionism has now

been conquered for Mendelism, i. e., for the genotype-

conception.

The genotype-conception here advocated does not pre-

tend to give a true or full ‘‘explanation’’ of heredity, but

may be regarded only as an implement for further critical

research, an implement that in its turn may be proved to

be insufficient, unilateral and even erroneous—as all

working-hypotheses may some time show themselves to

be. But as yet it seems to be the most prosperous leading

idea in genetics.

Heredity may then be defined as the presence of iden-

tical genes in ancestors and descendants, or, as Morgan

says in full accordance with this definition: ‘‘The word

heredity stands for those properties of the germ-cells

that find their expression in the developing and developed

organism.”’’

And now it is time to end this communication, too long

for its real contents, but too short for the importance and

diversity of the great problem of heredity.

In concluding this address I must highly emphasize the

eminent merits of Hugo de Vries. His famous book ‘‘ Die

Mutationstheorie,’’ rich as well in positive indications as

in ingenious views, has been the mediator for the new and

the old era in genetics. This monumental work is a land-

mark in the progress of our science. Like the head of

Janus it looks at once forward and backward, trying to

reconcile—at least partly—the antagonistic ideas of con-

tinuity and discontinuity in evolution and heredity; hence

a great deal of the charm of De Vries’s work. But just

these qualities have made the work of De Vries too

eclectic for the stringent analytical tendencies of modern

genetics—a tendency which has in recent years found a

true home in American science.

THE GENOTYPE HYPOTHESIS AND HYBRIDI-

: ZATION?!

PROFESSOR E. M. EAST

HARVARD UNIVERSITY

Ir sometimes seems as if the hypercritical attitude had

become an obsession among biologists. A proper judi-

cial spirit is of course essential to science, but do not

biologists often require a large amount of affirmative

data before assenting to a proposition which is in real-

ity a simple corollary of one already accepted?

For example, Darwin emphasized small quantitative

variations as the method of evolution, although he rec-

ognized the occurrence of larger changes both quantita-

tive and qualitative. De Vries, on the other hand,

emphasized large variations—especially qualitative

variations—as the real basis of evolution, although he

too admitted the existence of lesser changes. He dis-

tinctly states that a mutation or new basis for fluctua-

ting variation, may be so small that it is obscured by the

fluctuations themselves.

If relative frequency of occurrence is a criterion of

the value of variations in organic evolution, which is not

necessarily so, Darwin’s point of view is probably the

nearer correct. If one could find a unit basis for describ-

ing variations in terms of the physiological economy of

the organism concerned, i. e., if one knew exactly what

was a large change and what was a small change, he would

probably find that a random sample of inherited varia-

tions followed the normal curve of error. By this I

*Read at the symposium on the ‘‘Genotype Hypothesis’’ at the meeting

of the American Society of Naturalists, Ithaca, N. Y., December 28, 1910.

Contribution from the Laboratory of Genetics, Bussey Institution of

Harvard University.

The experimental results are from cooperative work between the Con-

necticut Agricultural Experiment Station and the Bussey Institution of

Harvard University.

160

No. 531] THE GENOTYPE HYPOTHESIS 161

mean that small variations would center closely around

a mode, and large variations would occur with a rela-

tive frequency inversely proportional to their size. The

point that I wish to emphasize, however, is that neither

Darwin nor De Vries recognized the proper distinction

between a mutation and a fluctuation. Darwin made no

distinction. De Vries, however, considered fluctuations

to be linear; that is, to be limited to increase and de-

crease in characters already present. He thought that

selection of such variations brought about changes in

the selected population due to the inheritance of the

fluctuations, but that the selected populations returned

to the mean of the general population after selection

ceased. Mutations, on the other hand, were gains or

losses of entire characters—qualitative changes—which

were transmitted completely, i. e., were constant, from the

beginning. De Vries did indeed state that mutations

could take place in any direction, which would involve the

idea of linear change or quantitative mutations; yet it

seems quite evident from his general attitude in ‘‘Die

Mutationstheorie’’? that to his mind qualitative and

quantitative variations were quite distinct.

Many practical breeders had long known, however,

that the selection of linear variations often produced

new races which were as constant as any races, provided

they were not exposed to crossing with individuals of

the general population from which the selected race had

come. Why this was true was unknown. It was felt

that there was a real distinction between certain varia-

tions, to which Darwin had not called attention; yet it

was felt that the De Vriesian idea was not wholly cor-

rect. It has been in making this distinction clear-cut and

definite that Johannsen has rendered his great service.

His elaborate extensions of the genotype conception of

heredity have cleared up many debated points, and

corroborative evidence has been received from so many

lines that it can hardly be doubted that the main points

of the hypothesis are correct. It may seem, therefore,

162 THE AMERICAN NATURALIST [Vou, XLV

‘as if the superstructure of this conception were too

elaborate to rest upon a simple foundation; yet I can not

see but that the basis of the entire hypothesis is the fact

that a fluctuation is a non-inherited variation produced

upon the soma by environmental conditions, while the

inherited variation, the mutation if you will, is any

variation qualitative or quantitative, that is germinal

in character. This being so, it seems scarcely necessary

for an elaborate proof of the proposition, for it is noth-

ing but a corollary to that part of Weismannism which

was already generally accepted.

Of course it is recognized that pure Lamarckism still

has followers to whom neither Weismannism in any

form nor the genotype conception of heredity could ap-

peal. But to thorough Weismannians and to those who

believe in occasional germinal response to environmental

conditions, it seems as if both propositions must be ac-

ceptable and their interdependence apparent.

Let us follow this line of reasoning to its logical con-

clusion in regard to the physiology of heredity. The

Mendelian notation has been generally accepted as a con-

venient way of accounting for the facts of heredity in

certain markedly discontinuous characters. It has been

questioned by many, however, whether the Mendelian con-

ception is not rather an apparent interpretation of a rela-

tively small number of facts than a general law. De Vries

has even suggested that there are definite physiological

reasons why certain characters should Mendelize and

others should not. His idea is that Mendelian segrega-

tion occurs when a germinal determinant for a character

(Anlage) meets an opposing determinant, and when no

such opposition exists the character in the cross-bred

organism breeds true. Now the universal tendency of the

facts of breeding is towards an interpretation the oppo-

site of this. When a determinant from one parent meets

with no such determinant from the other parent (pres-

ence and absence hypothesis), Mendelian segregation

appears. When the same determinant is received from

No. 531] THE GENOTYPE HYPOTHESIS 163

both parents, segregation can not be proved, for the char-

acter breeds true.

In fact the many results of experimental breeding dur-

ing the past few years have convinced me that De Vries’s

general conception of this matter is incorrect. There may

be finally a considerable modification of our ideas regard-

ing the ultimate nature of Mendelian unit characters and

the exact meaning of segregation, yet the universal appli-

eability of a strict Mendelian system to interpret the

facts of heredity becomes more and more apparent every

day. And the point that I wish to emphasize is that

Mendelian inheritance is a genuine corollary of the geno-

type hypothesis if the latter is applicable to a popula-

tion in a state of natural hybridity. In my work with

maize where free intercrossing does occur I am convinced

of the existence of genotypes in a state of natural

hybridization. Furthermore, these genotypes can be iso-

lated by inbreeding. If it were true, then, that only

certain markedly discontinuous characters such as color

Mendelize, how could genotypes which differ from each

other in size characters be isolated? It is not expected,

however, that the statement that Mendelian inheritance

and the genotype hypothesis are interdependent will be

received without proof. Data that are believed to fur-

nish such proof are submitted here.

When Mendelism was a new idea it was natural that

the behavior of many hybrids should be regarded as

irreconcilable to such a system of interpretation. The

earlier criticisms arose largely through the misconception

that dominance instead of segregation was its essential

feature. Later, when so many complex results from pedi-

gree cultures were fitted into a strict and simple Men-

delian notation, it was objected that the investigators

could by expert juggling of a sufficient number of factors

interpret according to their system any experimental

results they might obtain. Perhaps a few biologists re-

garded as a personal affront the gradual growth of the

idea that the facts of heredity were complex, but it is

164 THE AMERICAN NATURALIST [Vou. XLV

hardly likely that many could regard this complexity as

an invention of Mendelians. The latter would only too

gladly have the facts as simple as possible.

There have remained, however, several instances in

which hybrids apparently did not segregate in the F,

generation. Mendel himself investigated one such case,

the genus Hieracium. The investigation of Ostenfeld?

made this case perfectly clear by showing that the hy-

brids reproduced apogamously. Such asexual reproduc-

tion may also explain the behavior of hybrids between

species of brambles which are also said to breed true in

all their characters. These cases, however, and others

among animals of which human skin color is the example

par excellence, may be left out of consideration because

no exact data concerning them have been forthcoming.

There remain the experiments of two careful investi-

gators who observed no segregation in the F, generations

of their hybrids, those of Lock? upon heights of maize

plants and those of Castlet upon weights and ear lengths

of rabbits. Lock expected that if segregation occurred

it would be into two classes, i. e., simple mono-hybridism.

For this reason he made no measurements which would

show whether he obtained the kind of segregation which

as is shown later in this paper, does occur in maize hy-

brids. Castle® has recently admitted the possibility that

his numbers were not large enough to prove definitely

that segregation involving several small unit characters

does not occur in the ear length of rabbits.

The difficulty attending this earlier work was that there

was no way of explaining different manifestations of the

same character. Segregating characters could always be

interpreted either as the presence and absence of a uni

* Ostenfeld, C. H., 1904, ‘‘Zur Kenntnis der Apogamie in der Gattung

Hieracium,’’ Ber. Detach, Bot. Ges., 22: 7

* Lock, R. H., 1906, ‘‘ Studies in Plant Breeding in the Tropics,’’ MI,

Experiments with Maize, Ann. Roy. Bot. Gard. Peradeniya, 2: 95-184.

* Castle, W. E., et al., 1909, ‘‘Studies of Inheritance in Rabbits, ”” ’ Car-

negie Inst. Wash. Ta, 114: 5-70.

*In lectures at the Tawi Institute, Boston, Mass., 1910.

No. 531] THE GENOTYPE HYPOTHESIS 165

giving a 3:1 ratio, or as the complemental action of two

different units each allelomorphic to its absence, giving

:3:3:1 ratios or modifications of them. Nillson-Ehle®

and the writer,’ however, have shown that several units

each allelomorphic to its own absence may be the determi-

nants of what appears to the eye as a single character.

In the above paper the writer suggested that if such

ratios as 15:1 and 63:1—di-hybrid and tri-hybrid ratios,

respectively—were found in considerable numbers, then

higher ratios of this kind might account for the apparent

constancy of hybrids in characters that seemed to be con-

tinuous. For, if—as is quite probable—the additional

units increase the activity of the character in question,

and if there is no dominance,’ it is quite evident that

hybrids may be intermediate between the two parents.

All the pure classes in a complex character of this kind

would indeed be difficult to isolate, but segregation could

be absolutely proved by a comparison of the variability

of the F, and F, generations.

Since writing the above paper I have obtained clear

evidence of 15:1 ratios in two other cases. The first is

a red pericarp color, the second is the condition of endo-

sperm in maize which gives dented seeds as distinct from

that which gives flinty seeds. There is even considerable

probability that higher ratios oecur which affect the latter

character. In another paper? I have shown photo-

graphic evidence of size segregation in varieties of Nico.

tiana rustica and stated that similar evidence of segre-

gation of size character in maize had been obtained. The

following figures and tables show sufficient of the evi-

dence from the maize crosses to demonstrate conclusively

° Nillson-Ehle, H., 1909, ‘‘Kreuzungsuntersuchungen an Hafer und

Weizen,’’ Lunds Universitets Årsskrift, N. F., Afd. 2., Bd. 5, Nr. 2, 1-122.

' East, E. M., 1910, ‘ʻA Mendelian RF OAN a Variation that is

Apparently Canthmous: ?? AMER. NAT., 44: 65-8

° One. dose, i. e., receiving the dante gene Sit: a single parent, would on

the average increase the manifestation of the character half as much as

two doses,

. M., 1910, ‘‘The Rôle of Hybridization in Plant Breeding,’’

Pop. Sci. Pa Oct., 1910, pp. 342-354.

166 THE AMERICAN NATURALIST [Vou. XLV

that size characters segregate. It is hoped that this evi-

dence will make us more cautious about accepting uncor-

roborated statements about characters which are definite

exceptions to the Law of Mendel. It is by no means

certain that no such exist, but no experimental proof of

hybrids non-Mendelian in character has been made.

A further proof of segregation of size characters has

recently been made in a preliminary note by Emerson."°

He states that definite segregation occurs in beans,

gourds, squashes and maize. His full data are therefore

awaited with great interest.

Table I shows the frequency distribution of the heights

of plants in a cross between no. 5 a medium-sized flint

maize and no. 6 a tall dent maize. Sufficient seed was

obtained in a previous season so that the entire series

could be grown in rows side by side during one summer.

This procedure eliminates any possibility that the varia-

bility of the F, generation might have come from varying

conditions of soil fertility.

It will be noticed that the F, generation is nearly as tall

as the taller parent. This increase in size is not due to

dominance. It is the increased vigor that comes from

crossing in maize, and while it obscures the hereditary

differences in size, it is really a problem of development

and not of heredity as was shown in a previous paper.”

The distribution of heights in the F, generation is seen

by simple inspection of the table to be more variable than

the F, "generation in the case of each ear planted. Re-

duced to simple terms by the calculation of the coefficient

of variation in each case, however, the two generations

can be compared more accurately. In the F, generation

the C.V.—8.68 + .553 while in the various F, genera-

tions from different ears the coefficients of variation run

from 12.02 + .559 to 15.75 + .684.

* Emerson, R. A., 1910, ‘Inheritance of Sizes and Shapes in Plants,’’

AMER, NAT., 44: 739-746,

“ East, E. M., 1909, ‘‘ The Distinction lien Development and Hered-

ity in | Inbreeding,” AMER. NAT., 43: 173-18

167

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168 THE AMERICAN NATURALIST [Vou. XLV

Table II shows a similar distribution of heights in

cross between no. 60, a dwarf pop maize commonly known

as Tom Thumb, and no. 54, a sugar corn known as Black

Mexican. The distribution of heights of no. 54 was ob-

tained in the same season as the F, generation. They

were both grown upon the same plot of ground in which

the soil appeared to be quite uniform. Unfortunately,

the exact distribution of the heights of no. 60 and of the

F, plants which were grown in previous seasons, is un-

known. The range of the variates shown by the black

lines, however, is correct. Furthermore, from notes re-

corded at the time we know that the F, generation was

comparatively uniform, the greater number of variates

being distributed around classes 67, 70 and 73 inches. In

this case, also, the effect of crossing is shown by the rela-

tively high plants of this generation. The plants of the

F, generation show a wide range of variation. ‘he

highest individuals are practically the height of the

highest individuals of the taller parent, no. 54. The

lowest plants of F, do not reach the lower range of no. 60.

I interpret this as due to continued heterozygosis in other

characters and to physiological correlation. By the latter

term I mean that since the plants of no. 60 are very small,

F, segregates of the same size could only be expected

where the ears and seeds also are very small. But since

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tion in new combinations, normal growth correlation

probably resulted in a somewhat larger average size.

For example, little 40-inch plants were found with ears

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likely that such plants might have been smaller if they

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Table III and Figs. 1-4, show the lengths of ears in the

cross just described. In making this table the best ear

from each plant that bore a well-filled ear was taken.

The small ears, therefore, do not represent poor, unfilled

or supernumerary ears. The coefficients of variability

169

THE GENOTYPE HYPOTHESIS

No. 531]

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170 THE AMERICAN NATURALIST [Vou. XLV

Fig. 1. No. 60, female parent, illustrating variation in length of ear (4).

have again been calculated, but they hardly emphasize

the real segregation as well as do the photographs which

were made from representative ears of the different

classes found in the actual crop.

Table IV shows the segregation of weights of seeds in

F, in this same cross. Fig. 5 shows the average size of

Fic. 2. No. 54, male parent, illustrating variation in length of ear (p).

No. 531] THE GENOTYPE HYPOTHESIS 171

Fic. 3. Variation in length of ear of F; generation of cross between

No. 60 and No. 54 (4).

the seeds of the two parents and the F, generation and

the extremes of the F, generation. In making the

weights for this table, it was necessary to use a scheme

by which the sugary wrinkled seeds of the Black Mexican

parent, no. 54 could be weighed as starchy seeds. This

*

Sabet tae Be ae

Fic. 4. Variation in length of ear of F, generation of cross between

No. 60 and No. 54 (})

172 THE AMERICAN NATURALIST [Vou. XLV

was done by planting the no. 54 between rows of the

hybrid. Sufficient crossed seeds which had become

starchy through Xenia were obtained to make the weights

given. Not all of the ears, however, had 25 starchy seeds,

which accounts for the small number of plants meas-

ured. Furthermore, the seeds of no. 54 were a rather

mixed lot, which of course resulted in a higher varia-

bility than would probably have been found if only seeds

Fic. 5. Average size of seeds of No. 60 and No. 54 and the F, generation of

the cross between them. Extremes of the F generation.

of the individual plant of no. 54 which was used as the

male parent of the cross, could have been planted. Per-

haps it should be noted here since the question might

arise, that since the size of the seeds on an ear is gov-

erned by the development of the pericarp, the sugar corn,

no. 54, was unaffected in other ways than by having the

pericarp filled out with starch by the hybridization which

occurred attended by the resultant Xenia.

In Tables III and IV the measurements and weights of

the F, generation were recorded from only one cross,

although three crosses between the two varieties were

made. It might be said that one has the right to com-

No. 531] THE GENOTYPE HYPOTHESIS 173

pare only the F, generation of cross of which the F,

generation is given. If this were granted our conclu-

sions in regard to segregation would be the same. It

might be said, however, that sufficient records were made

of the F, generations of the other crosses to know that

they differed but little from the family of which the data

were recorded. In addition, it is a fact that general

Fic. 6. Avers a ears of No. 60 and No, 58 and the F; ge ation of the cross

etween them, Extremes of the Fə generat

populations of the two parents were studied, and their

variation was undoubtedly greater than would have been

that of the inbred progeny of the three parent plants

of either variety.

An additional cross between Tom Thumb pop maize

and a small purple flint is illustrated in Fig. 6. The ears

pictures show the average size of the two parents and

the F, generation, and extremes of the F, generation.

In conclusion there are two points I wish to notice.

Unquestionable segregation in size characters has been

shown by comparison of the F, and F, generations. It

can scarcely be doubted that some of these segregates

will breed as true as the parent forms, yet one can

174 THE AMERICAN NATURALIST [Von XLV

scarcely do more than speculate in regard to the specific

characters that are concerned in developing either organs

or individuals of certain sizes. There are probably many

characters that interact together in developing certain

characters, although the actual determinants in the germ

cells may be transmitted independently. These interde-

pendent reactions during development obscure to us the

real causes and what we regard as independent char-

acters may be but indirect results of unknown causes.

For example, the ability to evert their starch when heated

has been the distinguishing character of the subspecies

called Zea mays everta, the pop maizes. This character

so called, however, is the resulting physical condition of

the starch caused at least partially by the small size, the

thickness and the toughness of the enveloping pericarp. .

For these reasons it may not be possible—at least very

soon—to point out even the number of characters con-

cerned in size developments. From the number of ex-

treme segregates obtained in each case I might venture

to state that the size of ear in the cross shown in Fig.

5 is apparently due to not less than three characters,

while the size of ear in the other cross pictured seems

to be due to not less than four characters.

NOTES ON GUNDLACHIA AND ANCYLUS

DR. WILLIAM HEALEY DALL

U. S. NATIONAL MUSEUM

AsrourT seven years ago,! in the Nautilus I called at-

tention to certain problems connected with the genera

mentioned in the title of this paper, and urged investiga-

tion of the subject from the hypothetical view of the two

following propositions: :

1. That Gundlachia is merely an Ancylus which under

favorable circumstances has been able to form a cal-

careous epiphragm and survive the winter, which ordi-

narily kills the great mass of individuals, and, while

retaining the shell of the first season, to secrete an en-

larged and somewhat discrepant continuation of it dur-

ing the second summer.

2. That not all Ancyli necessarily have the ability to

do this, but the practise may have developed in certain

small species; and in tropical regions where the dry

season takes the place of winter it is possible that sur-

vival may become more or less habitual with some of

these species.

In this connection attention may be recalled to the

estivation in dry mud behind a double epiphragm, in the

Bahamas, of Segmentina dentata Gould,? and to the ob-

servations of Erland Nordenskjold? on Ancylus mori-

candi Orbigny, in Brazil.

During the past four years I have received an inter-

esting series of notes by Mr. John A. Allen, of Cleve-

land, Ohio, connected with the Nungesser Electrice Works

of that city, who has for some time been domesticating

in small aquaria species of fresh-water shells, including

* Nautilus, XVII, No. 9, pp. 97-98, January, 1904.

*Smithsonian Miscell. Coll., Vol. 47, Pt. 4, No. 1566, pp. 446-448,

April, 1905.

* Zool. Anzeiger, XXVI, pp. 590-593, July, 1903.

. 175

I6 THE AMERICAN NATURALIST [Vou. XLV

Ancylus and Gundlachia. His observations extend over

some six years and his notes contain so much of interest

that it has seemed desirable to summarize and publish

his data, thus placing on record facts which may stimu-

late others to follow his example.

Mr. Allen was kind enough to send to the museum a

lot of Anacharis supposed to contain both Ancylus and

Gundlachia in the living state, and numerous specimens

of the former were observed in a jar to which the vege-

tation was consigned, immediately after it was filled

with water. We were not able to distinguish with cer-

tainty any Gundlachia, though some may have been pres-

ent, and the small aquarium was kept in good condition

to await developments. This was in December, 1907.

The Ancyli continued to exist in apparent health during

the winter. In May, 1908, they seemed to go into hiding,

but during the summer reappeared again in rather dimin-

ished numbers, while a few young ones were observed.

No particular change was noticed during the following

winter and spring. While absent during the summer of

1909, it became necessary to transfer the collections to

the new building of the National Museum and the aquaria

were set aside. After the confusion of the transfer was

measurably over, I examined the aquaria and, finding

nothing visible, had the contents of the smaller one

(about 8 X 4 X 10 inches in size) removed and submitted

to the most careful scrutiny, the sand at the bottom

being placed in a fine sieve for examination, but not a

trace of Ancylus remained. I concluded that there had

been sufficient carbonic acid in the water to completely

dissolve these fragile shells after death, and that some

unfavorable condition had exterminated the colony. In

the other aquarium, which was about eight times the ca-

pacity of the smaller one, the water had evaporated to

about half its normal quantity and no mollusks except —

a few small Lymnzas were visible, while the Anacharts

had suffered considerably by the adverse conditions.

This was towards the end of November, when it was

No. 531] GUNDLACHIA AND ANCYLUS 177

difficult to get any fresh weed except by purchase. Being

much occupied, I contented myself with having the

aquarium filled with Potomac water from the tap. A

short time afterward I was surprised to note a large

number of young Ancylus with clean translucent shells,

on the side of the tank. There had never been any

Ancylus in the aquarium except such as might have been

put in with Mr. Allen’s Anacharis. These had up to

February 22, 1910, grown rapidly and continued to flour-

ish, though the number then visible was only about half

that which was noticed in November. In April the

Ancylus completely disappeared again. I have not been

able to discover where they went to, as the most careful

scrutiny of the sparse amount of Anacharis remaining

has not revealed any on the stems or leaflets. None of

the specimens seemed to have formed any septum and

nearly all of them were carrying a small colony of five

or six minute hydroids on the posterior upper surface

of the shell. The shells in February were still too fragile

to admit of removal from the glass without crushing,

and most of them kept on the side away from the

window, on the sill of which the tank stood. They were

about 3.0 mm. in length, and remarkably active, moving

about on the glass with surprising speed.

Subsequently Mr. Allen kindly furnished me specimens

of all these stages in alcohol; and I also had the oppor-

tunity of seeing some specimens in alcohol which had

been sent to Mr. Bryant Walker and Dr. H. A. Pilsbry

in 1908, and which were obviously identical with those

sent as examples by Mr. Allen to me over a year later,

and Dr. Pilsbry thought also with specimens collected

at Rockford, Illinois, in the ancyloid stage. On account

of its relations to the Gundlachia it will be referred to

here as Ancylus meekiana, since, unless in the Gund-

lachia stage, it seems not to have been described.

Mr. Allen also sent a lot of the wild Ancylus collected

in the Thornburg lagoon and which he was disposed to

regard as something distinct from his aquarium ancy-

178 THE AMERICAN NATURALIST [Vov. XLV

loids. After a careful examination under the microscope

I have been unable to find any constant differences be-

tween shells of the same age, except that the larger

specimens of Ancylus seem to have grown continuously

and evenly, while those ancyloids which attained a

Gundlachia stage show the sharp contrast between the

separate stage and that with the expanded third stage

of the shell. As this is only what one might expect if the

Ancylus attained its full growth without interruption,

while the ancyloid becoming septate passed through a

resting stage and then began to grow again, I consider

this difference of no moment systematically. The young

Ancylus and the ancyloid of the same length appeared

generally quite identical, though I noticed that in both

the obliquity of the apex varied to some extent, being

more emphatically bent toward the posterior right side

in some individuals than in others.

Ancylus meekiana is, when young, for a time nearly

parallel-sided, the growth toward maturity being more ex-

panded than at first. The apex is behind the middle of the

shell and slightly inclined toward the posterior right-hand

side at maturity. The microscope reveals some very

feeble radial striae from the apex, mostly vanishing be-

fore they reach the base. The incremental lines are not

strongly marked and the shell when clean is of a pale

translucent yellowish color. At or near maturity the

shell assumes a more oval form slightly more expanded

in front than behind. The animal has short pointed ©

tentacles, well-marked black eyespots, and a bluish-white

color, except about the mouth, where the yellow-brown

jaws are laterally set and the buccal mass has a pinkish

color. The shell is about 3.6 mm. long, 2.3 wide, and 1.0

high. In the dark-colored specimens of the wild Ancylus,

on the inside, may often be seen a dark-brown line cor-

responding to the margin of the young Ancylus and

showing the more parallel-sided early outline.

Miss Mary Breen, who has been studying the anatomy

of the fresh-water gastropods of the District of Co-

No. 531] GUNDLACHIA AND ANCYLUS ' 179

lumbia, was kind enough to undertake the removal and

mounting of radule taken from specimens of the differ-

ent stages, as well as from the wild Ancylus. This was a

task of no little difficulty on account of the extremely

minute size of the organ. The radule of ancyloids, sep-

tates and Gundlachia were absolutely identical in ap-

pearance and in number of teeth, the formula 5-10-1-10-5,

holding good for all. The uncinal teeth are not gradu-

ally modified from the laterals, but change abruptly and

form a distinct band on each side of the radula. The

lateral part of Stimpson’s figure of the dentition of his

Gundlachia meekiana is imperfectly made out, and obvi-

ously inaccurate; due doubtless to the fact that he had

only a few specimens and a not very powerful microscope.

Unfortunately his original material was destroyed in

the great fire at Chicago of 1871.

An examination of the radula of a septate form, col-

lected in Nicaragua by Professor B. Shimek, showed a

similar radula but with one more uncinal tooth on each

side. In this case, unfortunately, while endeavoring to

transfer the minute object to a slide for permanent pres-

ervation, it mysteriously disappeared, and a trial with

a second specimen was no more successful.

The form of the laterals is fairly well given by Dr.

Stimpson, and the rhachidian tooth is correct in his fig-

ure; but the gradual modification and uncertain number

of the outer teeth of the radula do not agree with our

observations on the specimens from Ohio. Renewed

correspondence with Mr. Allen led to the preparation

of this paper, pending the continuation of his observa-

tions.

Since the different stages of Gundlachia need to be

carefully discriminated, I have adopted the following

nomenclature for them.

In the first stage, when the young shell has a laterally

compressed subconical shape without any trace of

Septum, and is to all intents and purposes, concholog-

180 THE AMERICAN NATURALIST [Vou. XLV

ically and anatomically, an Ancylus, I call the individ-

uals ‘‘aneyloids.’’

In the second stage when the base of the conical shell

is more or less closed by a flat horizontal septum con-

tinuous with the margin around it, I call the individuals

‘“septates. ”’

Lastly, when the animal in its second season begins to

form a marginal expansion external to the septum, and

with its longitudinal axis sometimes at a considerable

angle with the axis of the ancyloid shell, I reserve for

this stage, up to and including maturity, the term

**Gundlachia.’’

Mr. Allen kindly sent alcoholic specimens of ancyloids,

septates and Gundlachias from his aquarium for ana-

tomical examination. The posterior part of the foot en-

tirely hides the septum when the living animal on the

walls of the aquarium is examined through the glass.

Nothing to distinguish it from ordinary Ancylus is

visible in the soft parts. The creatures feed on the

microscopic alge, etc., which grow on the walls of their

domicile and when feeding the movement of the jaws and

radula can be seen with ease by means of a magnifier.

On the alcoholic specimens, on the exterior of the shell,

were many minute lenticular capsules which, from anal-

ogy with Neritina, Pompholyx, ete., were supposed to be

the ovicapsules. The very young shells are very trans-

parent and fragile. It is difficult to find them until they

have reached a length of over a millimeter, and so far it

has proved impracticable to detach them from their roost

without crushing them, they are so extremely fragile.

The smallest septate seen was slightly less than two

millimeters in length and the animal had entirely with-

drawn behind the septum, which covers more than two

thirds of the aperture.

The species in the Gundlachia stage agrees substan-

tially with the form described from the District of Co-

lumbia by Stimpson, under the name of Gundlachia

meekiana. Asin many other fresh-water shells the newly

No. 531] GUNDLACHIA AND ANCYLUS 181

formed shell is yellowish translucent, while the older

part, especially when the pond or aquarium has a muddy

bottom, often becomes darkened or even blackish, and

more or less covered by a growth of conferva. Mr.

Allen calls attention to the fact that the sharp line of

demarkation which separates the dark encrusted shell

of the septate from its translucent Gundlachia extension

in the final stage, is evidence that the growth is not con-

tinuous, but that a resting period of some duration sepa-

rates the two stages.

I have preferred for the most part to refrain from

theorizing on the inferences to be drawn from the data,

letting them speak for themselves. To me, however, the

facts tend strongly to confirm the hypothesis suggested

in the opening paragraphs of this paper.

GENERAL NOTES

The following notes are partly summarized from a

rather voluminous correspondence with Mr. Allen, ex-

tending over more than four years.

The Thornburg lagoon is an abandoned channel’ of

the Cuyahoga River. In 1903 the river was fairly well

stocked with Unionidæ, but soon after that date the con-

tamination of the river by drainage and sewage killed off

the naiad population. This contamination is not believed

by Mr. Allen to have seriously affected the water of the

lagoon, though for some reason it does not seem to be a

place favorable to vigorous growth of mollusks. It pro-

duces a dwarf Planorbis parvus, a poorly developed

Physa, a small form of Lymnea humilis modicella and a

scanty supply of Amnicola. It is nearly filled with

Nuphar on the leaves of which Ancylus is found; also

Ceratophyllum, Potamogeton, ete., occur, especially

where the water is shallow.

At one place the bank bordering on the lagoon is steep

and the water near it deep, so here even at low water

mollusks would never be left dry. There is another por-

tion of the lagoon where a wide zone, producing vegeta-

182 THE AMERICAN NATURALIST [Vor, XLV

tion on which Ancylus occurs, is sometimes left uncov-

ered when by dry weather the water becomes low. In

this part of the lagoon three Gundlachia were found.

In general the water of the lagoon is deep and constant,

but owing to the presence of these shallows the hypoth-

esis that the formation of a septum in Gundlachia may

be due to alternation of wet and dry periods can not be

wholly excluded.

Ancylus occurs in one to three feet of water where

Ceratophyllum is abundant. In the deeper water shore

there is more Nuphar and less fine vegetation the Ancylus

seems to be absent or rare.

Mr. Allen attempted to domesticate the Thornburg

Ancylus, placing many young ones in a 15 X 9-inch jar

stocked with Anacharis from the lagoon. Apparently,

all soon disappeared, although Lymnea and Amnicola,

coincidentally transferred, lived a long time.

NOTES ON THE SEVERAL JARS USED AS AQUARIA

The 15 X 9-inch Jar—This originally contained a

dwarf Nymphea which died. There was a mixture of

peaty and ordinary soil about three inches deep in the

bottom of the jar. This was stocked in 1906 with

Anacharis and some specimens of Vivipara. The date

of the first appearance in it of the ancyloid stage of

Gundlachia was not determined. February, 1907, individ-

uals were very numerous and, some being taken out to

save in the dry state, the septate form was discovered.

Mr. Allen had noticed the presence of the ancyloid form

some time before. The first date at which Gundlachia

had been obtained from the Thornburg lagoon was July

15, 1906, but Mr. Allen doubts if the copious swarm of

ancyloid individuals of Gundlachia could have originated

in the jar so quickly from individuals accidentally put

in at that time. Some of the vegetation in the jar had

been received from elsewhere in Ohio, and some from

another state. The ancyloid stage of the Gundlacha

can not be distinguished from the associated Ancylus by

No. 531] GUNDLACHIA AND ANCYLUS 183

the external features as seen in the aquarium. In Feb-

ruary, 1907, probably hundreds of the unseptate ancyloid

form were present. There were several Vivipara in the

jar that winter. Subsequently they were removed, Mr.

Allen thinking that they might consume the food supply

needed by the ancyloids. Having heard that the stunted

growth of aquarium mollusks might be due to the pres-

ence of their soluble excreta in the water, he thought the

removal of the Vivipara might have had some influence

in this way. However, the removal of the large snails did

not stop septation.

In the winter of 1906-07 the specimens of Planorbis

parvus in the jar were large and healthy. In the winter

of 1907-08 the individuals of this species appeared

dwarfed. The water in the jar was then removed and

replaced by distilled water. After that the Planorbis

(and Mr. Allen thought also the Anacharis) took on a

more healthy appearance. He thought that the concen-

tration of saline matter due to refilling loss from evapo-

ration with ordinary lake water might have been influ-

ential injuriously, and the transfer to distilled water

have lessened the tendency to septation.

In the winter of 1907-08 septate individuals of which

the exact number were not recorded were again found in

the jar. In January and February, 1908, the ancyloid

form was fairly plenty, though not so numerous as in the

previous year. In spring they became fewer and in May,

1908, there were none visible (although in a smaller jar

there were some). They reappeared in the first half of

June, 1908. July 3, 1908, an immature septate individ-

ual was taken, and another on July 20. On the theory

that the septum is formed during a resting stage, these

may have been forming during May, when nothing was

in sight. August 3, 1906, another specimen was taken.

January 11, 1909, a specimen was found which had be-

gun to add the third or expanding stage of the shell ex-

ternal to the septum. No mature Gundlachia were

taken from this jar during the winter of 1908-09.

184 THE AMERICAN NATURALIST [Vou. XLV

August 19, 1909, a minute ancyloid specimen was taken,

and another August 24. September 26 six ancyloids

were visible at one time, but were not disturbed. It was

noticed that the ancyloids came out in sight on the walls

of the jar more freely on cloudy than sunny days.

This jar, December, 1909, contains a dense and vigor-

ous growth of Anacharis, also plenty of fresh-water

algw. It stands in the factory room subject to the fall

of factory dust, and to the changes of temperature in

the room. When the room gets unusually cold the

ancyloids mostly retire out of sight, temporarily. De-

cember 9, 1909, two specimens with the third stage of

the shell partly grown were taken near the top of the jar.

A sudden spell of unusually cold weather having begun

two nights previous may account for the ancyloids hav-

ing gone, as they did, into hiding, but it was somewhat

surprising that the more nearly mature form had not

also hidden.

The 8 X 6-inch Jar—This had sand on the bottom and

was planted with Anacharis from the larger jar, carry-

ing with it Ancylus, Gundlachia and Planorbis parvus

in the summer of 1908. The following winter, having

nothing but sand and water to live on, the vegetation had

become rather attenuated and feeble looking. The ancy-

loids were few and perhaps not more than half as large

as those in the larger jar. January 19, 1909, two or three

immature septate specimens were taken from this jar,

and February 10 one about half grown. Very few ancy-

loids were seen about this time in this jar. February 11

two immature septate specimens were taken, being all

of either form which were at that time visible. Feb-

ruary 24, 1909, for the first time since the eleventh, a

small ancyloid was noticed. On the twenty-seventh one

moderate-sized but fully septate individual was taken

and one ancyloid seen. Another septate was taken

March 8, and March 11-13 a solitary ancyloid was

noticed.

Fearing that there was not enough stock in the jar to .

No. 581] |. GUNDLACHIA AND ANCYLUS 185

continue the race, March 15, Mr. Allen put in half a

dozen ancyloids from the large jar. March 29 a mature

septate was taken out, and it was noticed that the Plan-

orbis looked frail as if insufficiently supplied with lime

salts. October 11, 1909, two half-grown septates were

taken from this jar. In the winter (1909-10) the Plan-

orbis, for some unknown reason, completely disap-

peared.

From these data Mr. Allen concludes that about 80 per

cent. of the stock in this jar had assumed the septate

form, the conditions obviously being such as to stunt

both Anacharis and ancyloids. In the 15 X 9-inch jar

the vegetation is luxuriant and abundant, and the sep-

tate individuals produced were only about two to five

- per cent. of the ancyloids. From this Mr. Allen con-

cludes that the formation of a septum is promoted by

causes which tend to restrict or retard growth.

The 9 X 7-inch Jar—This has a mixture of sand and

soil at the bottom. There is plenty of algal growth, but

the Anacharis is not as vigorous as in the 15 x 9-jar,

from which it was stocked with ancyloids and Planorbis.

In the winter of 1906-07 it yielded two septates. The

winter of 1907-08 ancyloids were fairly numerous, more

so than during the first winter, but no septates were de-

tected. July 1, 1908, young fry, hatched that season,

were visible. March 8, 1908, a fine large mature Gund-

lachia was taken. The original ancyloid part was deep

black and the flaring expansion beyond it was colorless

and transparent. In the sand-bottomed jar the mature

Gundlachia is uniformly yellowish translucent, but in

the large jar with mud bottom the whole shell gets black-

ish. December 13, 1909, a census of this jar was at-

tempted. The day was dark and a count difficult, but the

result was six septates and two ancyloids, all eight being

small and immature.

A Jar without Planorbis—Thinking it might be de-

sirable to have a stock of the ancyloids not associated

with Planorbis, Mr. Allen, about February, 1909, when

186 THE AMERICAN NATURALIST [Vou. XLV

the Planorbis was not breeding, transferred some Ana-

charis and a number of mature ancyloids to a new

15 X 9-inch jar, taking care not to introduce any Plan-

orbis. May 3, 1909, the first ancyloid hatched in the jar

was noticed; it was about half the size of the parents.

Others appeared later. By December, 1909, the parent

stock had disappeared and the stock hatched in the jar

remains very small, indicating some unfavorable condi-

tion. The bottom of the jar was covered with a mixture

of ordinary and swamp soil, but the supply of swamp

soil used in previous jars having been used up, that in

the present jar was taken from another place, and may

have contained some unfavorable matter. The Ana-

charis in the jar is fairly flourishing, but there is no

green algal growth.

General Conclusions—The Gundlachia may repro-

duce before assuming the completely mature form. The

shell varies in apparent color in accordance with the

muddy or sandy character of the bottom soil, but the

dark coating in the former case is not incorporated with

the shell structure.

The ancyloid stage has a period of least activity im

May. In July and August the septates appear. In au-

tumn and early winter the third stage is developed, be-

coming mature and complete in February or March.

This course is, however, not invariable in the aquarium

or domesticated specimens, since Mr. Allen has taken

ancyloids in January or February, an irregularity prob-

ably due to temperature and which might not have oc-

cured in specimens under perfectly natural conditions.

It is not certain that the ancyloids detected by Mr. Allen

in July and August were the young of that season, since

the minute creatures are very difficult to detect in the

aquarium and can not be handled. They are so trans-

lucent in the younger stages as to be practically invisible.

However, it is probable that the eggs are laid during the

winter and hatched in the very early spring.

It seems likely that under average conditions only aà

No. 531] GUNDLACHIA AND ANCYLUS 187

small proportion of the individuals advance beyond the

septate stage; and also that, of the ancyloids, only part

reach that stage. It is also probable, from Mr. Allen’s

observations, that anything which tends to retard de-

velopment may coincidently increase the tendency to

form a septum.

Since there is a period of least activity in May, a nat-

ural observation year will be from one May to another.

Mr. Allen summarizes the results obtained during the

period, May, 1908, to May, 1909, as follows:

None being taken before July nor after the following

March, there were secured between July, 1908, and

March, 1909, inclusive:

9 X 7-inch jar 1 septate

15 X 9-inch jar 4 septates

total 15.

8 X 6-inch jar 10 septates

-= From August 19, 1909, to December 13, 1909:

15 X 9-inch jar 8 septates

fs 16.

9 X 7-inch jar 6 septates

8 X 6-inch jar 2 septates

Further correspondence, during February, 1910, af-

fords additional notes.

A lot of the wild Thornburg Ancylus in alcohol was

sent by Mr. Allen and, contrary to his expectation, on

careful comparison with his series of ancyloids from his

aquaria, no difference, beyond slight individual varia-

tions, could be observed in the shells of the two series,

while the radula and the soft parts, after repeated com-

parisons, seemed to be identical in both.

Mr. Allen especially notes that in the winter, 1909-10,

the septates were the prevailing form in his aquaria,

exactly the reverse of the case when the aquaria were

freshly established. The generation, which appeared in

ay and June, 1909, in the ‘‘Planorbis-free’’ jar, was

dwarfed was not in sight during the latter part of the.

winter, 1909-10, and may possibly have all died. Mr.

Allen attributes the poor success of this jar to the use of

188 THE AMERICAN NATURALIST [Vou. XLV

swamp soil from a different place from that previously

used.

February 15, 1910, being a dark day and therefore

favorable for the septates to be out of sight, Mr. Allen

counted those visible in the large aquarium. Six sep-

tates and one ancyloid were noted. This illustrates the

observation that (excepting the ‘‘Planorbis-free’’ jar)

the septate is the prevailing form this season, and is

promoted by causes which dwarf or retard growth.

After noting the inexplicable way in which fresh-water

mollusks sometimes appear and disappear from pools

where they occur, Mr. Allen further suggests that the

septate form may be a prelude to total disappearance of

the species from a given place.

Another count on February 17, 1910, gave three ancy-

loids and three septates in sight, which Mr. Allen re-

marks is the first time for a considerable period that the

two forms have appeared in equal numbers. In the large

jar every mature specimen seen this season has been

conspicuously bicolored, the ancyloid or septate part

being stained deep black, while the flaring extension is

translucent and colorless, indicating that a resting period

intervened between the completion of the septum and the

formation of the mature shell.

Three ancyloids seen February 17 were all translu-

cent and about the same size. There can be little doubt

that they date from the summer of 1909. Hence, Mr.

Allen infers that the blackened original shells of the ma-

ture Gundlachia date from the season previous.

TABLE FOR JANUARY AND FEBRUARY, 1910

Specimens taken or observed

Date Gundlachia Septates Ancyloids

Janvary 12 (hig jar) 6.60685 00 83 0

Jannar 19 Gio MY gk, 1 0

January 31 (small jar) ............ 1 0 0

February 4 (Qui y 2 0 0

February 5 (big tar) -A se. 3 1 0

February 6 (medium jar) .......... 0 2 0

No. 531] GUNDLACHIA AND ANCYLUS 189

My last communication from Mr. Allen, dated De-

cember 11, 1910, contains the following additional notes:

As I have already written there was plenty of A-form (ancyloids)

and no G-form (septates) visible in my original large jar last summer.

But, since the latter part of November, besides ancyloids in various

stages, young septates have been visible in fair abundance. I counted

about a dozen in sight at one time.

He concludes that ancyloids are present most of the

year, but only young ones in May and mostly also in June.

But septates appear to be a strictly winter form, that is,

the immature septate stage appears in August or later,

reaches maturity (Gundlachia) in February or March,

and disappears about the end of April, after which and

a shorter or longer interval the young ancyloids of the

season begin to appear in the jars.

If the hypothesis stated at the beginning of this paper

be well founded, it would explain why mature Gund-

lachias appear, if at all, usually as a few individuals in

any given locality, and their presence can not be counted

on, as in the usual case of fresh-water mollusks, and is

distinctly a rarity in the temperate regions of the conti-

nent, where there are no well-defined wet and dry seasons.

NOTES AND LITERATURE

MIMICRY

IN some ways it would be a pity if the theory that mimicry has

arisen through the operation of natural selection must be dis-

carded since it is so ingenious in itself and was originated and

fostered by such masters of theoretical biology. However, the

old order seems to be surely giving place to new, here, as in other

phases of the study of evolution. Since Wallace’s ‘‘Papilionide

of the Malayan Region”’ the case of Papilio polytes has been a

classic. The females of this butterfly are of three sorts: one like

the male polytes, one like P. aristolochie and the third like P.

hector. The two latter species are supposed to be distasteful to

insectivorous animals while P. polytes is supposed to be edible.

e two ‘‘models’’ are numerous in individuals and while ‘*P.

hector and the hector form of P. polytes are confined to India

and Ceylon, both P. aristolochiew and the aristolochie form of P.

polytes have a wider range eastward.’’ The case is complete and

has been convincing. :

However, Punnett! found that in Ceylon

The following statements may be taken as a fair presentation of the

facts:

1. In the low-country the male form of polytes female is at least as

numerous as either of the other forms, and may be the most abundant

of the three. ;

2. In the northeast of the island, in the hector country, the aristo-

lochiæ form polytes is nearly as abundant as the hector form, though its

model is at any rate exceedingly scarce.

3. Higher up-country, where P. hector is rare or absent and P.

aristolochie is common, the hector form of polytes is more abundant

than the aristolochi# form.

It is obvious that these statements are not in harmony with the ideas

of those who look to the theory of mimicry for an explanation of the

polymorphism that exists among the females of P. polytes.

His observations concerning the enemies of butterflies con-

firm those of other heterodox students, namely: that ‘‘as serious

_enemies of butterflies in the imago state birds may be left out of

*«¢Mimiery in Ceylon Butterflies, with a Suggestion as to the Nature of

Polymorphism,’’ Spolia Zeylanica, Vol. VII, Part XXV, September, 1910.

190

No. 531] NOTES AND LITERATURE 191

account,’’ that lizards ‘‘certainly do not appear to exercise that

nice discrimination with regard to butterflies which is necessary

for the establishment of mimicking forms on the theory of nat-

ural selection,’’ and that asilids are not averse to preying upon

** distasteful species.’

After pointing out that the resemblances on which the theory

was based are far less striking in living, moving specimens than

in their expanded museum state, he says

Apart then from the questions whether the resemblances in many

cases of mimicry are sufficiently close to be of effective service to the

mimic, and whether the action of natural selection can be regarded as

sufficiently stringent to have brought these resemblances into being,

there are still the following difficulties in the way of the acceptance of

the hypothesis of those who look to natural selection as an explanation

of polymorphic forms in Lepidoptera:

1. The attribution of selection value to minute variation.

2. The absence of transitional forms.

3. The frequent absence of mimicry in the male sex.

4. The inability to offer an explanation of polymorphism, where the

polymorphic forms ean not be regarded as mimics of a distasteful

species.

Moreover, the hypothesis assumes that minute variations of all sorts

can be inherited, a position which at present is lacking in experimental

proof.

The gist of the constructive part of his paper is as follows:

Natural selection plays no part in the formation of these polymorphie

forms, but they are regarded as having arisen by sudden mutation, and

series of transitional forms do not exist because such series are not

biologically possible. Polymorphie forms may arise and may persist,

provided that they are not harmful to the species, and it is possible

to look upon their existence as due to the absence of natural selection

rather than to the operation of this factor. . . . That polymorphism

m a species should so frequently be confined to the female sex has long

been remarked upon by those who study these matters, and the explana-

tion most favored is that the female, burdened as she is with the next

generation, is more exposed to the action of natural selection and in

greater need of some protective adaptation. The weak point of such a

view is that it does not explain why the male is not similarly protected.

Tn Connection with this problem recent Mendelian research on sex-

limited inheritance is highly suggestive. It has been shown that cer-

tain types of inheritance receive their simplest explanation on the as-

sumption that the female is heterozygous for a sex factor not contained

qn the male and that this sex factor may, on segregation of the gametes,

repel the factor for some other character for which the female is also

192 THE AMERICAN NATURALIST [Voi XLV

heterozygous. From the beautiful experiments of Doncaster and Ray-

nor it has been inferred that inheritance of this type occurs in the

common currant moth (Abraxis grossulariata), where a distinct color

variety, var. lacticolor, occurs. The factor for grossulariata pattern

appears to segregate against the female sex factor, with the conse-

quence that in only one type of mating, and that a rare one, is the

lacticolor pattern transmitted to the male sex.

Gametic formule are suggested and the conditions they im-

pose are mentioned, but no breeding work was done. Whether

the above explanation of the behavior of grossulariata is correct

or not and also the correctness of the suggested formule for

polytes are immaterial to the present discussion. It is now well

known that ‘‘mutations’’ do occur in the females of insects and

that the new characters can be transferred to the male by proper

breeding. But, why do the mutants of P. polytes resemble

greatly, even if they do not do so to such an extent as had been

supposed, other species? On account of similar anatomical and

physiological make up; or, in this case, did the proper gametic

couplings once take place so that the then new female type was

transferred to the males (as in grossulariata) and was there-

after continued with such other modifications as were necessary

to separate them taxonomically? In other words, the mimicking

species came first and gave rise to the model!

Mutation, in itself, is not the whole story. Granting it, we

must be given a reason for the mutant resembling something else

and while the amendment just made to Punnett’s paper may

earry for this case, the chances are against it and we can not

apply it to resemblances between species of different orders. In

this connection, however, there seems to be an important thing

which is often overlooked. It would be far more wonderful if,

among the thousands of new forms which have arisen, there were

no resemblances than it is that some of the forms are very much

alike.

As Punnett and others have pointed out, the same process

which brought about such a close resemblance between, for ex-

ample, earwigs (Orthoptera) and rove beetles (Coleoptera) that

they are frequently mixed in entomological collections doubtless

caused also the resemblances (here called mimicry because an

advantage can be imagined) between certain flies and certam

stinging Hymenoptera. If ‘‘chance’’ or ‘‘environment’’ is used

in the former case it is not unlikely that it applies in the latter

also. Frank E. LUTZ.

The Anatomical Laboratory

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Somatic Alteration: Its Origination and Inheritance.

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The Sp rey of Nave a tion Si Pure peas to Sex

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Vor. XLV | April, 1911 No. 532

GENETICAL STUDIES ON CENOTHERA. II

Some Hysrips or Cnothera biennis ann O. grandiflora

THAT RESEMBLE 0. Lamarckiana

DR. BRADLEY MOORE DAVIS

Tue status of Cnothera Lamarckiana is a matter

which must be given serious consideration in any attempt

to judge the value of De Vries’s mutation theory, for the

reason that the behavior of this form in throwing off

marked variants (mutants) from the type has been re-

garded by De Vries as direct experimental proof of mu-

tation. Indeed, the theory of De Vries may fairly be

said to rest chiefly upon the behavior of this interesting

plant, the account of which forms so large a part of his

work, ‘‘Die Mutationstheorie,’’ 1901-1903.

Aside from his claim of direct proof of the origin of

mutations from nothera Lamarckiana, De Vries offers

a considerable body of indirect evidence of the sort pre-

sented in Darwin’s ‘‘Variation of Animals and Plants

under Domestication,’’ and in that extensive and very

carefully sifted account of Bateson, ‘‘Materials for the

Study of Variations,” 1894. However, much of this in-

direct evidence of De Vries deals with the origin of

‘‘sports’’ from domesticated forms or with the origin

* Contribution from the Laboratory of Geneties, Bussey Institution of

Harvard University No. 7. An investigation conducted with aid from the

Elizabeth Thompson Science Fund for which the author desires to express

his indebtedness,

193

194 THE AMERICAN NATURALIST (Vou. XLV

of new forms under conditions that are not typical of

those of nature in the wild. For these reasons such evi-

dence could never appeal with so much force as would

direct experimental proof that a wild species is in the

habit of producing suddenly new types sufficiently dis-

tinct from the parent form to rank as new species or even

as strongly marked varieties.

In ‘‘Die Mutationstheorie’’ of De Vries the behavior

of Enothera Lamarckiana in giving rise to the so-called

mutants is presented as evidence that new species have

come into existence without intermediate steps from a

form which is assumed to be typical of a species in na-

ture. (Enothera Lamarckiana is made to bear the

weight of an elaborate hypothesis, treating of funda-

mental problems, very much as the apex might be made

to bear the weight of an inverted pyramid. As the equi-

librium. of the inverted pyramid depends upon the sta-

bility of its apex, so the value for the mutation theory

of the evidence from the behavior of Lamarckiana must

rest with the status of this plant as a form truly repre-

sentative of a typical species.

De Vries from the beginning took it for granted that

(Enothera Lamarckiana was a native American species

introduced into Europe, an assumption that was perhaps

not unnatural, although dangerous when the responsibil-

ity of direct proof of the origin of species by mutation

was laid upon its behavior. As far as the writer is

aware, O. Lamarckiana, as a wild American species, is

unknown. No American locality can be cited where it

may be found as a clear component of the native flora.

There are certain records of its presence under condi-

tions that indicate the possibility of its being sometimes

a garden escape, and there is some herbarium material,

referred to Lamarckiana, which, however, has not been

tested by culture and was collected at times when the im-

portance of the most critical judgment in identification

was not appreciated. It cannot be said that American

botanists are not alive to the importance of the status of

No.532] GENETICAL STUDIES ON (2ENOTHERA 195

Lamarckiana, for it is well known that a certain group

would follow with persistence any clue that might give

evidence of its being or having been an American native

species.

Crities of the evidence for De Vries’s mutation theory

have been aware of the point of weakness that lay in the

uncertain status of G@nothera Lamarckiana and the sug-

gestions of Bateson and Saunders (’02, p. 153), Hast

(707, p. 34), Boulenger (’07, p. 363), Leclere du Sablon

(710, p. 266), Tower (710, p. 322), and others have prob-

ably occurred to many, namely, that this plant is of hy-

brid origin and that the appearance of its ‘‘mutations’’

is due to the continued splitting off of variants after the

manner of hybrids. This view is held by a number of

American botanists with whom the writer is acquainted

and represents the attitude of those who are sceptical of

the importance of mutation as a factor of organic evolu-

tion in nature. If Lamarckiana is of hybrid origin it

should be possible to obtain evidence of its probable

parentage, and the present paper offers a hypothesis |

with a considerable body of evidence in its favor. After

the evidence has been presented the hypothesis will be

discussed in the concluding section entitled ‘‘The Pos-

sible Origin of @nothera Lamarckiana as a Hybrid of

O. biennis and O. grandiflora.”

None of the hybrids of biennis and grandiflora de-

scribed in the following pages are identical with La-

marckiana. There are important differences, chiefly of

foliage and stem markings, which distinguish the hybrids

at a glance, but on the other hand these characters in

taxonomy would be considered of minor importance and

the hybrids, if their origin were unknown, could not be

placed elsewhere than next to Lamarckiana. Further-

more, these differences are of a sort that are likely to be