A COMPARISON OF THE RESPONSES OF SESSILE AND MOTILE PLANTS AND ANIMALS PROFESSOR VICTOR E. SHELFORD f this most marvelous and complex chapter of life” and ‘‘the momentous issues involved” and “no more fundamental problem could well be stated” bear out this statement. The ardency which appears here and elsewhere in the discussion of scientific questions, appears to the writer to be associated with the discussion of problems which can not be referred to existing facts for solution. Few of the present generation of scientific men acquired a working knowledge of the methods of science before the age of twenty-five years, and the early habits of mind were formed in the atmosphere of the supernatural and dogmatic, which has characterized human thought for centuries. It is doubtful if the majority of us can maintain a scientific attitude for more than a short period; we must con- stantly come back to our tests and principles. This may account for many of the contradictions regarding scientific principles which one finds in the conversation of scientific men. When the methods of science have become the methods of society we may expect a group of scientific men far more effective than we ourselves can hope to be. 662 THE AMERICAN NATURALIST [Vol.XLVIII reactions. Intelligent behavior occurs in the lower* Arthropods. Even Paramoecium shortens the time re- quired to turn around in a tube, by repetition. Actions formerly regarded as instinctive now appear to be mere innate tendencies perfected by repetition. Thus the ideas of fixity have essentially disappeared from this field. The response of organisms to injuries and the general control of form in the lower groups has done much to break down the ideas of fixity developed by Weismann and embryological schools. Thus Child, the leading American worker in this line, is able to control size, form, number of eyes in the case of Planarians. Various writers have, found modifications inherited after several generations of repeated stimulation (see Bateson, ’13). The development of anti-bodies (immunity) has been shown to be a response occurring in connection with many normal processes. The discovery of responses of so many types has led to abandoning ideas of fixity even among students of embryology and genetics. Thus we note the recent decline of the doctrine of continuity and independence of the germ plasm and kindred doctrines and points of view, which constitute the central ideas of fixity. It will accordingly be profitable to consider some further facts which make the germ-plasm doctrine un- necessary. 5. Aspects of the Unten ability of the (term Plasm Doctrine The presence of primordial germ plasm is assumed even in sessile colonial organisms such as plants, coelen- terates, and in flatworms, etc., where under certain con- ditions any small part of the body may give rise to a complete organism. Here the theory is not needed to explain the facts. Child (’ll) said: The theory of the continuity of the germ plasm as a system, inde- pendent of the soma, except as regards nutrition, has played an im- portant part in biological thought during the last two decades, but I am convinced that it has led in the wrong direction and that it is re- No. 575] RESPONSES OF PLANTS AND ANIMALS 663 sponsible for many pseudo-problems of heredity and development, which on the basis of a different theory could never have occupied the attention and wasted the energy of biologists. Briefly my position is, that the gonad primordium is, at least up to a certain stage of develop- ment, physiologically a part of the individuality as are other organs, and that its further history of differentiation into male and female gametes indicates that it becomes specified in a particular direction, at least partly in consequence of its correlative environment in the or- ganism. The independence of the germ plasm is not well sup- ported physiologically. Thus Wilson (T2, p. 163) says of the effect of prolonged ingestion of alkaline salts by mice: No obvious changes were evident in the liver, kidneys, lungs, spleen and intestines but in the testes some extraordinary alterations were found. These results are of especial interest because as the cells of the testes except the basal cells are regarded by many cytologists as out of coordination with the somatic cells. As a result of these experiments it would seem that they are more susceptible to changes in reactivity than the surrounding plasma. Dungay (’13) and authors cited have thrown compara- ble light on this question. The facts of embryology themselves are but a pseudo argument in its favor. The organisms in which continu- ity is supposedly demonstrable are highly individuated and their organs highly specialized and many different organs are early separated from the common mass of cells. The germ cells thus follow the general law of development in such animals. The germ plasm is prob- ably no more independent of other parts of the organism than is the liver or any other special tissue. “Germ plasm” and “germinal continuity,” if such exist, may thus be merely incidental to the particular type of organi- zation of the specialized individuals in which they occur. It should further be noted that on the botanical side this doctrine of the independence and continuity of the germ plasm has received little attention and has been given little credence because “germ plasm” arises from different tissues and is neither set aside early from the soma nor is it in any other sense clearly continuous. 664 THE AMERICAN NATURALIST [Vol. XLVI1I Furthermore, the plasticity of plant structures made the application of the doctrine of natural selection to sup- posed adaptations untenable, and this type of explanation has received little more attention with botanists than have Lamarckian speculations with zoologists. The adaptation characters of plants can not ordinarily be used as taxo- nomic criteria (Coulter, ’08). 6. The Measure of Values in Biological Science One hears reference to pure science as something quite apart from applied science. It is indeed true that inves- tigators in pure science are to some degree prompted to push forward in research by interest in the problems for their own sakes. But the human mind does not work long isolated from practical affairs or the main channels of human interest, and it is doubtful if the pure-science investigator continues long in this way. Observations are soon connected up in some way, actual or possible, with some human interest, be it as remote as the improving of human stock in remotely future generations. Thus “pure science” defined as investigation for investigation’s sake hardly exists so far *as the pure-science workers are concerned, but may be best defined as an indirect method of attacking problems of general importance. It differs from applied science in that application to practical problems is not its aim, though the estimated value of theories and results in “pure” science are often greatly modified by applicability to practical questions. Certain problems and groups of facts in biology are sometimes referred to as fundamental. Some one has said that a fundamental problem is one the solution of which biologists have decided will give greatest progress. It is doubtless true that a few leaders reach such decisions with regard to particular questions, but the real causes of their general acceptance as fundamental are social and imitative. Thus when one investigator or a small group of investigators arrives at such a decision many others usually become active along the same lines largely because it is a popular topic. Thus under the influence No. 575] RESPONSES OF PLANTS AND ANIMALS G65 of a group of investigators among whom Weismann was a conspicuous leader, problems of the germ cells, the egg’s early development, and heredity, became “ funda- mental problems.” They evidently argued that since all comes from the egg and germ cell, all must be discover- able in the egg. If germ plasm were as independent from soma, as completely insulated from environment as con- tinuous from generation to generation as has been assumed, the study of germ plasm would be the only way to the solution of the problems of heredity and evolution. This follows no matter whether the chromosomes or almost the entire egg are credited with carrying heredi- tary qualities; only the postulation of continuity and independence from soma and insulation from environ- ment are necessary. If the independence of germ plasm from soma be accepted even in a weakened and modified form it follows that studies of somatic characters can at most be of secondary importance from the point of view of heredity and evolution. Thus in some quarters the value of various lines of zoological work has been esti- mated largely, unconsciously, no doubt, in proportion to the nearness or remoteness of their relation to. the “germ plasm” question. Thus it is true that in biology as in all other fields values are measured consciously or unconsciously by criteria. In recent years another better criterion of value has made its appearance among zoologists. The germ plasm criterion already discussed was primarily morpho- logical; the second is physiological, borrowed no doubt from physiologists. It measures values on the basis of the analysis of the organisms into terms of physics and chemistry or is concerned with a mechanistic conception of life in all its manifestations. From this viewpoint the study of each and every part of the organism is important because the discovery of laws governing one part is usually or at least often of general importance. Investi- gations from this viewpoint have shown that the germ plasm criterion is clearly illogical in its application to the study of somatic characters because it is based upon the 666 THE AMERICAN NATURALIST [Vol.XLVIII tacit assumption that the soma is governed by different laivs from the living matter which makes up the germ plasm from which it arose. In other words it is assumed that the germ plasm is so different from the soma that the discovery of laws governing the soma is a type of investigation of relatively little significance. Some criterion of values is of course necessary in sci- ence as well as elsewhere, and for the sake of argument we would be willing to accept the second when broadly stated and the first when broadened and modified so as to accord with the second as appears to be the case among certain students of genetics. In other words, problems of the germ cells, the egg, and heredity, are of much importance when the germ cells themselves are regarded as dynamic and in their relations to the dynamics of the organism as a whole. Granting that these are true and tenable criteria of values in present-day biological science, what is to be the method of application? Should biology demand . that results be of direct application to these “central” prob- lems? One has but to look at the history of almost any branch of science to find that great, if not the greatest, advances have come through following up results at points where relations to the central problems of the period were quite unsuspected, or by the transference of methods, principles and results from one field to an- other where relations between the two were not suspected. Take, for example, immunity and immunization, the his- tory of which is ably sketched by Adami ( ’08, pp. 451- 528). It has been known for ages that one attack of many infectious diseases yields more or less complete immunity from subsequent attacks. Thus for centuries in India and the East individuals, chiefly children, have been pur- posely inoculated with matter or by contact. The prac- tise grew out of experience showing that diseases thus communicated to healthy individuals from weaker ones are less severe. In 1796 the results of Jenner on vaccina- tion with cowpox were published. This may have influ- No. 575] RESPONSES OF PLANTS AND ANIMALS 667 enced Pasteur, who over eighty years later laid the foundation for the modern epoch of development, by combating a plague of diarrhoea in poultry (1880). During the twenty years following, various investigators added noteworthy contributions, and about 1900 Ehrlich and Morgenroth evolved the “side-chain theory ” by which a large number of possible conditions can be pre- dicted and all the observed facts of immunity explained. While not expressed in strictly chemical terms, the theory and the experiments which support it are very important both practically and theoretically. In recent years the knowledge of immunity and comparable phenomena have been greatly extended. Various workers (Pfeifer, Vol. II, p. 262) have shown similar phenomena in the .increased resistance of plants to poisons, thus making the responses of plants and animals still more generally comparable. Most recently workers on problems such as fertilization (Lillie, ’13), standing in close relation to the older germ- plasm’ doctrine, have discovered facts belonging to this field and made use of Ehrlich’s theory to explain the ob- servations. This development has helped to confirm the conclusion of some investigators that immunity phe- nomena represent important features of the chemical mechanism of life. Adami has remarked, That a plague of diarrhoea in a poultry yard, studied by a professor of chemistry, should be the seed from which has grown the vast de- velopment of later years is a strange fact, but a fact nevertheless. What was the attitude of pure science so called, of germ-plasm doctrinairies, and biologists generally during the long period which elapsed before they could make use of his results? CleaTly it was one of indifference, if not disgust, toward the subject. The probable result of such attitudes on the progress of the investigation of immunity phenomena, had it not been for their immense practical significance, is clear. They could not have received their proper share of attention. Thus in the pursuit of the analysis of the chemical mechanism of life men who sought it directly have failed in this one impor- 668 THE AMEBIC AN NATURALIST [ Vol. XLYIII tant step, and the chief contribution has come from very remote indirect methods. Generally speaking the inves- tigators who choose a direct method of attack often put themselves somewhat in the position of the chemist who would make chemical analysis of living matter when his first step defeats its own purpose by killing the substance to be analyzed. The failure of exclusively direct methods is often evident. Still the ability to obtain results by the method of direct attack, combined with a far too rare ability to tie with them indirectly obtained data, some- times gives noteworthy contributions. It accordingly remains to be seriously considered whether or not biology can afford to apply criteria to the measure of the values of investigation. Their application is of course largely unconscious, but the effects are not thereby modified. Noteworthy results of their applica- tion are (a) concentration of work in certain lines indi- cated by a given criterion, and ( b ) an actual abandoning to a large degree of remote and indirect methods of attacking the problems which the criterion involves. This means the partial abandoning of the methods for which pure science stands. Criteria can be safely used only in a very broad gen- eral way, and in application more often to past progress than to current investigation. They are perhaps most valuable as a guide to individual investigators working on problems remote from these more or less central “pure science” questions. That some guide should be in the hands of such workers is beyond question. In the hands of those attacking the problems directly they often appear detrimental because they soon take on an extreme form and become regarded as fundamental. At this stage they are usually in need of extensive revision. If the investigator is contributing observations and details only, he is doing a great service, for such information is needed everywhere. If he is able to combine his own and others results, he almost invariably draws data from all sources, direct and indirect , far and near. Granted the No. 575] RESPONSES OF PLANTS AND ANIMALS 669 ability to synthesize, the opportunity to nse the ability sometimes comes to those who attack the so-called cen- tral problems directly. It comes equally often (we believe more often) to those who have led np to the central prob- lem from some remote viewpoint, frequently condemned by the followers of direct method of attack. Granting the importance of synthesis, if the biologist seeks the solution of such a problem as the germ-plasm problem, he should encourage workers to start at points as remote from the subject as possible, that they may approach it with new light and from new angles. In judging the work of another, its value should be determined more by the (a) strictness of scientific method used, (b) the thoroughness and completeness of the in- vestigation, and ( c ) (and perhaps most important of all) evidence of ability to synthesize and combine other re- sults with his own with a view to broader generalization. It must, however, also be recognized that there are many biological problems of much human importance, which must be solved quite independently of the ideal central problems of pure science. 6. Summary and Conclusions From the data presented above, we note that the doc- trine of purposeful, advantageous response (including anthropomorphic ideas) arose from the uncritical non- experimental study of the responses (structural) of ses- sile and (behavior) motile animals. The idea of the all- sufficiency of natural selection is largely the outcome of observational study of apparently fixed and yet appar- ently adaptive characters of motile highly individuated animals. The doctrine of the continuity of the germ plasm is likewise the outgrowth of the study of highly individuated animals in which the various organs are early differentiated in the dividing egg. No one of the doctrines is wholly tenable ; no one is more than a partial truth. Each appears to have arisen from a recognition of certain more or less unconsciously selected and un- critically interpreted phenomena by each of several men 670 THE AMEBIC AN NATURALIST [Vol. XL VIII who secured different facts and attempted explanations. In a few animals the “germ plasm” may be morpho- logically early differentiated and reasonably continuous, though governed by the- same laws as other tissues. In others, any part of the general tissues may give rise to a complete organism. The behavior of some organisms is intelligent and purposeful, while that of others is largely mechanical. Some structural responses of sessile organ- isms are advantageous, some indifferent and some harm- ful. Some of the more fixed structures of the highly indi- viduated animals are advantageous, some indifferent, and some disadvantageous (Metcalf, ’13). No other type of general statement appears to be tenable, yet each extreme of each proposition has at some time or other been the subject of some all-inclusive doctrine. Such are the limitations of an individual’s knowledge and the psychic limitations of our race and generation. In considering the psychology of religion, Ames ( MO, p. 394) points out similar well-recognizable tendencies in that field of human activity and quotes Cooley on social development as follows : Much energy has been wasted or nearly wasted, in the exclusive and intolerant advocacy of special schemes — single tax, prohibition, state socialism and the like, each of which was imagined by its adherents to be the key of millennial conditions. Every year makes converts to the truth that no isolated scheme can be a good scheme, and that real prog- ress must be advanced all along the line. Advance all along the line is what biological science must achieve. This I believe means the encouraging of all lines of indirect attack, whether they at first throw light on the ideal central question of pure science or important practical problems or not. It means the exer- cising of extreme caution in the application of criteria of values to scientific results. Such measures tend not only to stifle the best initiative in good investigators, but also tend to check the building up of fruitful hypotheses. The latter danger is greatest in connection with the mechanistic criterion referred to above. As has already been stated, criteria of values can be safely applied only No. 575] RESPONSES OF PLANTS AND ANIMALS 671 as broad general guides, and investigation should be measured on the basis of its thoroughness, the originality shown, etc. In science special schemes of course do not exist recog- nized as such, but intolerant application of criteria of values results in essentially the same condition. One often hears the statement made by so-called scientific men, that this or that line of investigation has been pur- sued for several years, but has failed to yield important advances or generalizations, but they add, we will be very glad to recognize it as soon as its value is proven. This seems to us* to be a distinctly unscientific attitude, and but a polite modern statement of a spirit which in former generations often sent men to the stake or dungeon. This is true because to these polite objectors its value is rarely or never proven. It is “schemes” (preconceived theories) thus presented that have in the recent past stifled the study of responses by discouraging efforts in that direction and thus contributed materially toward making zoology the unorganized science which it is to-day. We must recognize that the various aspects of zoology pure and applied have never been well corre- lated, less so we believe than in any other branch of natural science, clearly less than in botany. In general, animal physiology has been isolated in medical schools and genetics, faunistics and morphology have not been properly influenced by it, while morphologists for many years held themselves aloof from other workers. In a discussion dealing mainly with the doctrine of natural selection in the origination of adaptations, Mathews (’IS) has sounded the keynote of a growing attitude toward all response questions. Out of the infi- nite different combinations which may enter into the proteid molecule and the varying rates at which metabolic action may go forward, innumerable types of irritability and correlated structure have been and still are arising under the influence of environment external and internal. Of these some are incompatible with life, others indiffer- 672 THE AMERICAN NATURALIST [ Vol. XLYIII ent, and others advantageous. Upon these physiological characters natural selection has operated to eliminate, and with time has perhaps rendered of less frequent occurrence, those characters that are incompatible with their conditions of existence. External form, color orna- mentation, etc., while no doubt often of importance them- selves are more often the advantageous or indifferent correlatives of physiological or irritability types which are compatible with their conditions of existence. The study of irritability and response may be pursued in many ways — by experiment, by observation in nature alone or combined with experiment. The mapping of stimulating conditions in nature, of the distribution of types of irritability and response, which is one function of field ecology and modern geography, can hardly fail to contribute materially to the advance of knowledge in many lines, including that of the physico-chemical mechanism of life. The student of experimental ecology has an infinite field of problems and methods thrown open to him by the organization of such information relative to responses. 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