# Smithsonian Report/1898/The Relation of Plant Physiology to the Other Sciences

THE RELATION OF PLANT PHYSIOLOGY TO THE OTHER SCIENCES.
By Dr. Julius Wiesner, Rector of the University of Vienna.
Most Worthy Assemblage: In entering upon the honorable but also responsible office of rector of our university I shall first perform the duty of thanking my honorable colleagues for the trust which placed me in this position of high esteem.
Few institutions have outlived the century so vigorously as the rectorate of this university, which has become more and more strengthened by the course of time. The reason for this lies not only in the purposeful end of this office, but equally in this, that each rector placed in the balance his greatest possible sacrifice toward the fulfillment of his task of representing, for the time, this highest academical honor. So each rector has become an example for his successor for the most conscientious fulfillment of duty. So accrued to the office an authority which will make it possible to exercise a discreet power in fulfilling the assumed responsibilities, as well as in upholding the honors and rights of the office when sustained by the wisdom of the academic senate, by the willing cooperation of all colleagues, and by the trustful demeanor of the academic youth, who have always found in the rector the promoter and chosen solicitor of their true interests.
In the alternation of faculties, and in view of the alternation between members of the mathematical-natural-science and of the philosophical-historical groups of professorships (a principle observed by common consent in the philosophical faculty), the rectorship after a period of five years fell to a representative of the first-named scientific group. I am grateful from a special combination of circumstances for the honor of bearing the rectorate in a year in which Austria celebrates the fiftieth-year jubilee of His Majesty the Emperor. You have just heard from the lips of my honored predecessor what preparations have ​been made by the academical senate during the preceding collegiate year for a celebration worthy of this rare occasion.
But the jubilation of the anniversary has suddenly turned to deep sadness. We still stand under the dazing influence of the horrible deed by which our noble Empress was torn from us, and we sorrow deeply with our sorely tried august Monarch, to whom we all owe so much, and not least our university.
During the more than five hundred years of its existence, the University of Vienna has passed through no more brilliant epoch than the half century just closing. We are surrounded by speaking witnesses—the building in which we gather for work and for celebration, the grandest palace that was ever built for a university, and a corps of instruction which is scarcely rivaled in the whole world.
Most of the professorships and our university institute were founded during the reign of our present Emperor, including the professorship which has been intrusted to me—exactly a quarter of a century. This was the first regular professorship of plant anatomy and physiology, not only in Austria, but above all, in any university.
In following the time honored requirement of delivering a lecture in the field of one's specialty upon the occasion of entering into the new office, two themes especially present themselves—the development of plant physiology and its present status. Since both subjects have been recently and thoroughly discussed, I have decided to take for the subject of my present address one allied to and scarcely less interesting than those, namely, "The relation of plant physiology to the other sciences."
In the narrow limits of the time allotted to me I can only attempt to sketch in a few strokes the essential features in the reciprocal action between plant physiology on the one side, and on the other side other natural sciences and the social and mental sciences, and to make clear that plant physiology represents not merely a branch for a few specialists, but that it is aided in its advance by the other sciences; that in turn it contributes to advancement in various fields of science and practical life, and, finally, that it reaches out as a many-branched whole into the Universitas literarum.
In my present address I shall use the term "plant physiology" in its broadest sense, as the whole system of teaching relative to the structure, development, and life of plants.
Like all other sciences, plant physiology has developed in response to the demands of life. As physics and chemistry had their basis in the industries, so plant physiology grew by each experience gathered from agriculture, horticulture, and sylviculture. Even if the origin of plant physiology be not historically demonstrable as a result of the demands of practical life, still a portion of our terminology would bear witness to the correctness of the assumption. Expressions like grow, blossom, and graft, designations such as leaf, stem, and root, were not ​introduced by botanists, but originated in practical life and passed over from the popular vocabulary into our science.
The first demonstrable beginnings of plant physiology we find among the Greek philosophers, chiefly Aristotle and Theophrastus. But in these beginnings there was no developmental capacity. In our inductive developmental period it was necessary to lay a new foundation for the doctrine of plant life. The Englishman, Stephen Hales, in the beginning of the eighteenth century, was undoubtedly the founder of plant physiology in general, and especially the founder of physical plant physiology, while the commencement of chemical plant physiology is to be referred to the Hollander, Ingenhouss. Ingenhouss is closely identified with us in this regard, that for years he resided in Vienna as physician of the Empress Maria Theresa and of Emperor Joseph II. Some of his first contributions to plant physiology were worked out in Vienna—a fact little known. Later, until the middle of this century, the science was advanced by investigators of French nationality, foremost the Swiss investigator, De Saussure. At the present time, all civilized nations, the Japanese not excluded, take part in the advancement in this field. But if in our time names like De Saussure and Boussingault stand as towering monuments and the teachings of Darwin cease not to influence our physiological conceptions, there have been for many decades German plant physiologists who stood not simply as compeers of their French and English colleagues, but without exaggeration one may venture to say that German investigators have assumed the leading role in the solution of the most important questions.
The present developmental period in natural sciences, so rich in unprecedented results, is characterized by the inductive method of research and by the principle of the division of labor. It required thousands of years to show mankind that the experience of all knowledge takes root, and that the human mind, with its limitations, despite the genius of occasional great men, can only by the combined work of many, each deep in his narrow specialty, arrive at the solution of the great problems of science. As a consequence, we see in all fields of research the modern socialism of scientific progress vanquishing the intellectual giants of the olden time.
The objections to the principle of the division of labor in behalf of the mental stage of the individual are well known. These are gradually disappearing, and I will leave them without discussion. But for the development of science all of the weaknesses and failures resulting from this principle will be eradicated, as I shall later demonstrate by certain examples at hand.
In the realm of botany the division of labor brought about first a separation of descriptive botany from the studies directed toward general morphology and physiology, which latter, reenforced in a measure, placed themselves in rather sharp opposition to the descriptive side. ​In his epoch-making Elements of Systematic Botany, Schleiden, near the middle of the century, challenged the systematists in these words: "The time has passed wherein a man who could give the names of 6,000 plants would because of that be called a botanist, but another who knew 10,000 plants would be designated a greater botanist, and the formerly so-called systematic botany has been thrust back into its proper place of simply a hand servant of the true and exact sciences." But the systematists returned the thrust. One of her foremost representatives declared to the men of the "true science:" "If one were to collect all the positive results thus far offered by plant physiologists it would scarcely suffice to fill a nutshell." Wrong judgments lay here on both sides, such as are always called forth by insufficient knowledge and limited insight into the relation of things. The principle of the division of labor led here, as usual, first to a separation of two so closely related territories, and it was only as one of the later results of the application of this principle that they were again brought into their natural relations.
The science, however, incurred no lasting injury from the fact that descriptive botany and physiology first pursued opposite ways. In each field good constructive material was accumulated. An earlier commencement of common constructive work would only have led to complications.
A really gratifying prospect is presented when one considers how gradually systematic botany was advanced by this branch of physiology in its widest sense. Linnæus and his school could still content themselves with a very elementary form of plant description, form and position of leaves, number and arrangement of flower parts—in short, any character which a plant in flower presented to the naked eye sufficed for the end of plant description as then pursued. Now, however, a hundred thousand species of plants are known. Of orchids alone there are as many species as all the species of plants described by Linnæus put together, and it is easy to see how the few superficial characters at first used for distinction of species became wholly inadequate. Besides, descriptive botany could not content itself with simply distinguishing plant species and supplying them names.
Furthermore, it became necessary to consider the systematic arrangement of the ever-increasing species. There had also to come into play that great principle of natural science investigation which one of our most distinguished colleagues has called the "economy of science." When I speak of orchids I express the sum of all those characters which are common to these 8,000 species. This expression of the sum of common characters must possess this quality, that by it I can distinguish this plant group from all others and, besides, express their relationship to other groups. The sum total of isolated characteristics must be brought into the simplest, briefest expression possible. Linnæus sought to attain this "economy" by his artificial system. This ​was a good key for the determination of species while the number was still small, but it was far from being a natural system of plants. In order to attain to such a system, one had to dig deep into the development and the inner structure of plants. This permeating of systematic botany with general botanical knowledge raised this study to a height where it might with propriety be called the earlier systematic botany.
The separation of plant species proceeded, therefore, no longer, as it did earlier, upon the basis of external characters, but came to be more and more promoted through the facts furnished by anatomy and embryology. That pure physiological characters, i.e., characters that find expression in the life processes of the plant, should be brought forward to distinguish species is one of the latest discoveries. A physiological character of plants would formerly have been held as unreal. Distinguishing characters were wanted which were always to be found in dead material, such as lies in our herbaria. So long as that sort of character sufficed there was nothing to be said against the proceeding. Now, however, we meet plant forms whose scientific nature is to be recognized only in their life activities. A Swedish botanist has made the observation that rust fungi exist which on morphological characters are impossible of separation, but are characterized only in this, that they will live on one or a few species of grasses, but will not develop when transferred to other grasses which are hosts for fungi of exact morphological equivalence. The well-known black rust of grain (Puccinia graminis) occurs upon wheat, rye, oats, barley, and several uncultivated grasses. It was formerly supposed that the grain rust could choose at will between these species of grasses. This is, however, not the case. It is known, for example, that the rust of rye can develop on barley, but not on wheat and oats, and it is evident that several physiological forms of grain rust may be distinguished upon this ground.
So in the progress of research has come about a union between two branches of botany which appeared widely separated, so widely that it was formerly supposed that the chasm between them would never be bridged over, i.e., between systematic botany and physiology in its broadest sense—indeed physiology in the narrowest sense of the doctrine of function. It is plain that all other fields of botany stand in reciprocal relation with physiology, but it required a long time for this state of things to come about.
Nothing would seem more natural than that in scientific investigation a plant form and the function of its organs would be equally considered—to consider it as a machine, whose parts are arranged for a purpose and in their combined action accomplish an intended result.
One need not wonder, therefore, that investigations undertaken at an earlier time, with the purpose of making clear the agreement between form and function of the plant organ, wholly miscarried and led to vague speculations and barren telleology. It was in the midst of our ​inductive research period when these natural philosophical speculations sought to establish themselves. Once again it was the return to the inductive method and to the principle of the division of labor which cleared the way to real progress. There came about a sharp sundering of morphology from the doctrine of function—so sharp that it was regarded as dangerous and punishable for one of these subjects to deal with things pertaining to the other. Under the chastisement of Schleiden no one attempted to demonstrate the functional significance of a morphological structure. Narrow minded as this method of procedure appeared, it was to the purpose. Embryology of plant organs arose out of these conditions, and physiology was gathering richly of usable constructive material for the future.
Only a small part of morphology, which we botanists call anatomy, but which is identical with the histology of the zoologists, developed along with physiology. The greater part of morphology, which corresponds to what zoologists call anatomy, pursued its way independently of physiology.
I venture to raise the question here as to why zoology and botany have not chosen the same expression for analogous branches of their science; why under the term "anatomy" botanists and zoologists designate different things. The cause of this lies again in the principle of division of labor, which at first always leads to a sharp separation, and only after advances in scientific work does it bring about union. The development of botany proceeded independently of zoology, and vice versa.
Terminology, taken at the beginning, is not of such serious importance, but subsequently it would be in accord with the "economy of science" if in related subjects similar expressions were employed to express similar concepts. That will come to be the case; and even now in botany the expression "histology" begins to be used in the same sense as in zoology.
The collaboration of working material in the form of demonstrated facts on the side of morphology, as well as in the realm of the doctrine of function, has aided in bringing the two nearer together, and the solution of the questions as to the functional significance of morphological structures is in full tide. The most successful has been the union of morphological and physiological knowledge as regards plant tissues, the study of which, as previously mentioned, was from the first often entangled with the doctrine of function. In this way has arisen in recent times the much cultivated branch of botany to which has been given the name of physiological plant anatomy.
No field of research stands so near plant physiology as does animal physiology. Where run, above all, the boundaries of these two territories, when, in the lower stages of plant and animal organisms, it is no longer possible to distinguish with certainty between plant and animal, and when investigations are ever revealing new ​identities between plant and animal life? To-day we know that plants respire in the same sense and for the same purpose as animals; indeed, the forms of respiration are the same in both kingdoms. Besides ordinary respiration in which free oxygen is taken up, there is, in plants as in animals, a so-called intramolecular respiration, in which fixed oxygen in highly oxidized compounds serves to carry on respiration. The newer investigation has acquainted us in no equivocal way with the power of motion—yes, even with the sensibility of plants. Slow movements which are to be detected by change of position during growth are common in plant life, but even very lively movements such as are exhibited by swarming of certain reproductive cells (swarmspores and spermatozoids) occur frequently in the lower groups of plants. And shall one not speak of sensitiveness in plants when it is shown that external influences such as light, gravity, etc., act as an irritant which the plant receives, conducts to parts more or less distant and responds to by some definite movement or in general by some definite reaction?
The principle of the division of labor has worked here as elsewhere n the natural sciences, first separating and then bringing together. Plant physiology has gone its own way, as has also animal physiology, the one not concerning itself about the other; and only enlightened minds have first discerned the inner identities of both, and felt themselves compelled in the solution of fundamental problems to reach out for data into the apparently foreign territory of the other. Thus, one of the greatest animal physiologists of the new era, Ernst von Brucke, who once occupied this same place of honor, to which investigator we are indebted for three great fundamental contributions in the field of plant physiology.
When investigation in each of the two fields had yielded a rich fund of usable data and had placed them in an orderly arrangement, the union of the two—plant physiology and animal physiology—began. When one takes up a recent work on animal physiology he discovers with satisfaction that already much consideration is given to the facts and conclusions of plant physiology. Recently certain works upon general physiology attest the natural association into which animal and plant physiology have entered.
The relations of physics and chemistry to plant physiology lie so closely before us and are so well known that I need not here go into nearer details concerning them. But that both these great fields of investigation stand in reciprocal exchange with their younger sister, plant physiology, I will illustrate by a characteristic example. One of the foremost living plant physiologists investigated the working of osmotic force in the life of a plant. He soon had to learn that, however much the physiologists had contributed to the knowledge of this question, both in elementary and advanced works, it was not sufficient for his purpose, and thereupon it was thought necessary by him to ​deal with a whole series of questions in osmotics from the standpoint of pure physics. As a result, an insight was attained by which the significance and explanation of numerous processes in plant life could be arrived at. Moreover, the experiments of this plant physiologist formed the foundation upon which was built the now famous Van't Hoff's theory of osmotic pressure, which, according to this theory, comes about in a way analogous to that of gas pressure. This is not the first time that plant physiologists have taken up the question with helpful results in the theory of osmosis. The genial and many sided Dutrochet, the discoverer of "exosmosis and endosmosis," was in the front rank of plant physiologists.
As with chemistry and physics, plant physiology stands also in this relation of reciprocal exchange with meteorology and climatology. How greatly plant life is affected by meteorological conditions and how the distribution of vegetation is dependent upon climate is evident every- where, and rich is the knowledge which plant physiologists have gained by the application of the teachings of these two sciences. But in certain investigations relating to the life processes of plants these teachings did not suffice, and so, on the part of plant physiologists, many climatological and meteorological questions had to be taken in hand. For example, one physiologist, in order to learn the mechanical effect of rain, i.e., to find out the exact force of large rain drops on leaves, determined the weight of the heaviest rain drops, the velocity of fall, and the working force of falling rain. Likewise, contributions to a more exact knowledge of the importance and significance of light to plant life were made by plant physiologists.
The connection between science and life has never been so conspicuous as now at the turning of this century, and will doubtless become yet more striking in the next century. Proud overbearance on the one hand and a capacity for misunderstanding on the other have often and for a long time maintained a sharp antagonism between science and practical life, which rested with both sides on insufficiency of knowledge and narrowness of view. Really great investigators always recognize that, as Helmholtz opportunely expressed it, knowledge alone is not the end of mankind upon the earth, but that knowledge should be applied in the affairs of practical life. Only in this sense is knowledge power, as Helmholtz thoughtfully added on the same occasion.
The great botanical reformer, Schleiden, declared in the middle of the century to his fellow-botanists, who absolutely disregarded the application of botany in practical affairs: "All the industries which make use of vegetable stuffs in manufacturing, etc., in doubtful cases ask in vain of botany for information, although it is in a position to direct and advise the industries, but it has no practical knowledge to give; knows least, often, the very plants which furnish the most important stuffs, and borrows even from artisans themselves every​thing outside of the circle of that systematic botany which deals only in nomenclature."
This rebuke did not pass without effect. A student of Schleiden's, the honored anatomist, Hermann Schacht, taught how to identify the commoner fibers used in spinning by microscopical characters. Soon from Austria strong impulse and effective work appeared along these lines, where, by the' use of methods of investigation practiced by plant anatomists, the foundation was laid for technical microscopy and the technical study of raw material in the plant kingdom, which two studies were first placed in the curriculum of the technical high schools of Austria.
Through the use of plant physiology in questions of practical life this science came to be an aid in the administration of justice. The courts request from plant physiologists as from chemists professional opinions, and more than once has the botanical institute of our university been in a position to respond to the requests of the court.
Botany, as is well known, came early to be a strong aid in the medical science, which encouraged not plant physiology but systematic botany—in fact, called it into existence. What the diggers of roots and herb dealers in the Grecian age began, Hippocrates and other Grecian physicians continued, namely, the search for plants with healing qualities, the naming and distinguishing of which appeared in the most thoroughly collaborated materia medica of Dioscorides. Until the period of the reawakening of the arts and sciences, this work formed the chief source of botanical knowledge. The repayment of this great debt of botany to medical science was made, however, not so much by the immediate debtor—systematic botany—but chiefly through plant physiology. Let the science of medicine always remember that the subject of bacteriology, now become so important, owes its origin to botanists. It was not merely that bacteria were first differentiated by botanists, it was likewise a botanist, the late Ferdinand Cohn, director of the Institute for Plant Physiology in Breslau, who first recognized bacteria as the cause of diseases. It was he, also, who originated the well known generic names of bacilli, micrococci, and bacteria. What importance bacteriology has come to assume in the diagnosis and etiology of disease, for hygiene, and other branches of medicine is generally known.
Likewise those branches of plant culture which gave the first impulse toward the establishment of plant physiology have in turn been richly repaid for all the suggestions and usable facts which they furnished. Agriculture, forestry, and horticulture are to-day permeated by the spirit of plant physiology, and what these practical studies have gained in scientific insight is for the most part due to plant physiology. It must be said also that agricultural chemistry has contributed materially to the principles of plant culture, but the one​sidedness of the perceptions of chemical analysis, which drew conclusions as to the soil nourishment for vegetation only by comparing soil analysis with plant analysis, could only yield a one-sided solution of the question at issue, particularly that of plant nutrition. Not until synthetical research as to the nutrition of plants made upon living specimens could it be determined on the side of the plant what elements taken up from the soil serve for food, what of the material taken up is used for other purposes, and what is merely neutral. Thus agricultural chemistry, under the influence of plant physiology, has become transformed into agricultural physiology, which to-day is to be counted one of the most important studies that contribute to practical life.
The fruitful cooperation of scientific learning and of agriculture and industry may be illustrated by the following instructive example: Long before Liebig's time the farmer knew that the cultivation of leguminous crops would make the soil richer in nitrogen, in that nitrogen compounds accumulate that which can be assimilated by plants. It was also known that leguminous plants produce peculiar little tubercles on their roots, which were explained in most varied and circumstantial ways. Bacteriological investigation has shown that these tubercles constitute the habitat of certain bacteria, which obtain entrance into the roots of leguminous plants, and live there in the mutually helpful relation of symbiosis. These bacteria, which live in peas, lentils, lupines, etc., possess the remarkable capacity of bringing the nitrogen of the air contained in soil into compounds which can be assimilated by plants. Thus the old riddle was solved. If beans be planted in sterilized soil they grow less vigorously than in ordinary soil, which harbors the bacteria in question. Abundance of these peculiar bacteria in the soil increases the productiveness of leguminous crops. This knowledge has resulted in a new industry. In the famous dyeworks of Meister & Lucius, in Hochst, is generated a product called "nitragin" for the cultivation of lupines, peas, and other legumes. This "nitragin" is simply artificially increased bacteria of different species kept in the resting stage, which, added to the soil in which lupines, etc., are planted, increases the available nitrogen supply.
Similarly numerous other sciences were richly repaid in practical help by plant physiology for what they had first furnished for "working capital" in the form of knowledge and stimulus. Therein, however, the account between theory and practice is not settled. That great account will, indeed, never be canceled. With the advancement of agriculture, of commerce and industry, arise continually scientific problems, and new scientific learning and discoveries ceaselessly promote practice. Ever more and more is disappearing the old opposition between science and practice, and more and more the opinion matures that human progress rests upon the harmonious cooperation of both.
The invasion into the realm of practical life by plant physiology has ​called forth many relationships between it and the social sciences. What it has done in explaining the exhaustion, what it has contributed to the understanding of the significance of the forest covering for climate and for the cultivation of field and garden vegetation has benefited the social sciences. But there are besides many other relations existing between these two seemingly widely separated sciences. In order further to illustrate this I will give another example, intentionally an extreme but instructive case. For almost a century men busied themselves with the question as to how long the earth's stores of coal would last in view of the enormous increase in the use of fuel. The estimates awakened grave apprehensions, though one might reassure himself by this fact that the premises upon which such dire conclusions were based lacked very much of being accurate. Next, comes from across the ocean a more disturbing and vexatious intelligence. Through the American and English papers goes the news—reflected also in the German press—that the danger of extinction of mankind would come sooner than had hitherto been feared. Under an appeal to the authority of a great physicist it was claimed that, with the increasing consumption of mineral fuel by the various industries, all supplies of mineral coal would be exhausted within five hundred years. But the last remnants of coal—so it was further claimed—it would no longer be possible to bring out of the earth, because in the meantime the oxygen of the atmosphere, as a result of the enormous increase in combustion, would have decreased to such a limit that the air would no longer be adapted for human respiration.
The computations in question seemed to be entirely accurate, but again the assumptions were uncertain, upon which these terrible results were predicted, as indeed the whole question whose solution proceeded upon complications of a similar kind, were dealt with only from the chemical standpoint, quite disregarding the character of living organisms.
Every condition of the earth which corresponds with the Kant- Laplace theory forms the starting point for computations like those above cited. All of the earth's carbon is burned up; all of the oxygen allotted to our planet is exhausted. After cooling of the earth, the green vegetation appears and generates free oxygen under the influence of sunlight. This hypothesis derives the whole of the atmospheric oxygen from the green vegetation. Since, at that time, there was no other natural source of oxygen upon the earth besides the green plants, it followed that with increasing combustion the oxygen supply would diminish. In order to check this decrease it was advised that extensive areas of fruit trees should be planted. So it was hoped that in this way a sufficient quantity of oxygen and human sustenance would be assured to help out the inhabitants of the earth. What small agencies opposed to the harmonious working of the powers of nature!
Upon how weak a foundation the foregoing hypothesis stands may ​be seen from the fact that a totally opposite conclusion may be drawn from applying the premises in field experiment, with the use of certain well-established facts of plant physiology. It has been shown, for example, by the French plant physiologist, Boussingault, that the volume of carbon dioxide taken up by green plants is exactly equal to the volume of oxygen given off in the presence of sunlight. So if, as supposed, all the oxygen of our atmosphere were liberated from carbon dioxide by green plants then would the quantity of carbon dioxide of the earth's atmosphere have been seven hundred times more before the appearance of green plants than at present, while the proportion of oxygen, according to this hypothesis, would have increased from 0 to 21 per cent in volume, while the enormous proportion of carbon-dioxide would have fallen to its present mass, namely 0.03 per cent in volume. If one were to go so one-sidedly into such conclusions as happened in the hypothesis above cited it would be possible, under the assumption of such an enormous decrease of atmospheric carbon dioxide, to under- take beforehand to predict the disappearance of vegetation, indeed to foresee that both organic kingdoms—the plant and the animal world— were so ordained as to maintain continually a reciprocal influence upon each other, and the capacity of adaptation of plants and animals, bordering on the wonderful, would make possible their continuance under external conditions widely different from the present.
But the discovery of Boussingault teaches another thing. Since the quantity of carbon dioxide in the atmosphere is practically constant, namely, an average over the earth of about 0.03 per cent in volume of the atmosphere, and since the succession of elements upon the earth will not be interrupted (i.e., carbon dioxide, through combustion, respiration and putrefaction, is constantly being produced, and also through green plants—whether on this side of the world or at the antipodes—is constantly being reduced to oxygen by the agency of light), this gas can scarcely increase to a greater proportion than 0.03 per cent in volume because so constantly involved in transformation, and even a much higher rate of combustion than is now prevalent would scarcely alter the great surplus of oxygen. An important feature our question has thus far been only, briefly referred to—the extraordinary capacity of organisms of adapting themselves to their environment. If the proportion of carbon dioxide in the atmosphere should notably increase because of the consumption of coal, the plant world would still adapt itself to these changed conditions. This adaptation must, however, be granted to those whose hypothesis leads to such dire consequences as previously depicted; for they must concede that the earlier vegetation of the earth endured a far greater proportion of carbon dioxide than at present, and indeed made use of it. But when the capacity of plants to adapt themselves to the proportion of carbon dioxide in the atmosphere is conceded, then the increased ​consumption of coal Deed lead to no disquietude, at least in so far as there will be no diminution of oxygen in the atmosphere.
I have dealt thus at length with this illustration, because I wished through it to indicate to what false conclusions one-sided assumptions and problematic suppositions can lead. The problem in question here is much more complicated than is often supposed, even by prominent scientists, and to the objections which I have already urged against this doctrine of disaster very many more may be added, though it must be said that the matter was never taken very seriously in scientific circles.
In the impulsiveness of its youth, natural science has framed still many other one-sided suppositions when dabbling in strange territory. Thus Liebig ascribed the downfall of the world-embracing Roman Empire to the exhaustion of the soil, to the lack of phosphoric acid and potassium in the cultivated land, brought about by "robber farming," i.e., by too-continuous overcultivation of the soil. With propriety Du Bois- Reymond rejected this theory; but, on the other hand, the historian could not agree with this critic when he said: "Roman culture disappeared because it was built upon the quicksand of aesthetics and speculation." Du Bois-Reymond likewise attempted to solve a complicated phenomenon by too simple a formula.
Inadvertently we have just touched upon the relations of the natural sciences to the mental sciences, especially of history. For a long time these relations were very uncongenial, and insufficiency of knowledge and narrow conceptions upon both sides have often enough led to severe strife. The first attempts of naturalists to engage in the solution of historical problems from their point of view, and of historians—I recall here above all Buckle—to make use of natural history teachings in historical research, did not turn out well, and on that account could scarcely contribute toward an intellectual intercourse between the two "camps," as they were referred to frequently in those times of strife. It happened more frequently that these efforts suffered a severe rejection. So the saying was: "With the knife of the physiologist one may not cultivate the hard soil of history, but to that end is needed the strong plow of the historian." Or, an eminent historian relates that it had been made clear to him that history could not permit itself to be molested by Darwin and his associates.
An eminent historical investigator who once occupied this place of honor published very recently a work on genealogy. This, the author himself said, built the bridge between the historical and the natural sciences. In this work the effort is made to present systematically genealogy as learning in all its various relations to historical, social, political, judicial, and natural science questions.
The animal physiologists as well as those of botany have busied themselves not a little with the question of the determination of sex, ​but they have considered this question from the ontogenetic standpoint, if I may so express it; they have simply asked. "What conditions of the parents and what influences upon them lead directly to male or to female progeny"? In the above-mentioned work on genealogy the question is philogenetically treated, if I may thus again express it. The author raises the question, namely, whether inheritance is not of significance in the determination of sex; whether, to express it plainly, certain fathers or mothers, because of prominent deep-rooted peculiarities, are not destined to produce either wholly or chiefly either male or female offspring.
It is no idle fancy which our historian has brought forward for the statement and proof of this question; on the contrary, with astonishment one sees by an examination into this work on genealogy how the author has gone into the finest natural science problems of inheritance, into the subtilest phenomena accompanying creation and the beginning of sex, in order by thus bringing forward in support all available knowledge to give the greater value to his work.
The genealogical method here brought into use by the author is worthy the high consideration of biologists. He studied the genealogical history of numerous families of the nobility and found as a rule that in one, male, in another, female, descendants so predominate that the tendency toward inheritance of sex within a family can scarcely be called in question.
For further biological studies the following discovery resulting from genealogical investigations ought to be of significance: That in the human family the male element is of more weight in the formation of sex than the female.
Similarly other branches of knowledge that stand as aids to history e.g., diplomacy and paleography, the same is true also of archæology, have come to hold certain relations to the natural sciences. The study of the physical characteristics of old documents, of the substance written upon and the material used in writing, was undertaken earlier by the historians themselves. Now, microscopists of various special fields, foremost among them plant physiologists, have taken up this task; they cleared away old errors like the charta bombycina (paper made of cotton which is supposed to have preceded that made of rags), the charta corticina which proved to be papyrus, and many others, and traced the cloth or rag paper, so important to civilization, back to the eighth century of our era; whereas the historians could trace it only to the fourteenth century, and show that this paper was first invented neither by the Germans nor by the Italians, but was due to the oft illustrated inventive genius of the Arabs. Thus the history of paper was placed by the skillful work of plant physiology upon a new basis whose certainty, tested by the historical researches of the foremost historical and linguistic students, has met with fullest acknowledgment.
Plant physiology also rendered active assistance in the construction ​of a not unimportant bit of the history of civilization. In this direction, meanwhile, there had appeared early botanical contributions. For instance, I would recall that a professor of botany in our university, my ever-remembered teacher, Franz Unger, renowned as a plant physiologist, submitted important contributions toward a knowledge of the origin of the various cultivated grains and other cultivated plants of importance to mankind during his botanical incursions into the field of the history of civilization.
In this very territory of the history of civilization the most widely differing branches of mental and natural science become associated. For example, by such associated investigation was demonstrated the distribution of the most important cultivated plants from Asia to Greece and Italy, and from here over the rest of Europe.
The origin of wheat is lost in tradition; the Greeks considered it as a gift from Ceres, the Egyptians as one from Isis. Neither from the historical nor from the linguistic point of view is there any indication as to the origin of wheat. But the physiological character of this cereal shows that its original home must have been in the Steppes.
Again, the native habitat of barley is shrouded in darkness. But on the other hand, on linguistic grounds, the native habitat of rye—which, like wheat and barley, is one of the Steppe grasses—is to be sought between the Alps and the Black Sea.
The distribution of many of the more valuable species of fruits from western Asia through Italy to us has been confirmed on historical, linguistic, and natural science grounds. The home of the peach (persica) lies in Asia, perhaps, as the name signifies, in Persia. In the days of the Roman republic the peach was unknown, and is first mentioned in writings of the first century of the empire. The culture of the peach tree in Italy was begun and prosecuted by slaves and freedmen from western Asia, who, moreover, established the famous fruit-culture of the Romans.
Likewise the cultivation of vegetables spread from Italy over Europe, as the names of many vegetables show; for example, the name "kohl" for our commonest vegetable (cabbage) is taken from the Latin word caulis.
Plant physiology, like every science, whether it be only through bringing forward explanatory figures or through systematic contribution, has stepped into association with philosophy. The attempt to gain a conception of the molecular or micellar structure of the make-up of cells, or through direct observation to disclose the ultimate life unit of the plant through known facts, belongs, as does the origin of invisible atoms and molecules, in the region of metaphysics; that is, they are within the province of philosophy.
​Perhaps I shall not be accused of going too far if, finally, I consider a moment the somewhat phantasmically spun threads which bind plant physiology with psychology. I have in mind that work of Fechner, the founder of psychophysics, published in the stormy year of 1848, a book written with the tenderest human sympathy. It had been formerly thought that plants were incapable of locomotion, and on that basis were distinguished from animals. This view was refuted by the same facts which destroyed the long-held opinion as to the insensibility of plants. Now, the last year has brought valuable explanations of the power of sensation in plants, and many fancies of Fechner's as to the sensibility of plants have been transformed into scientifically grounded views. The reception and conduction of stimuli and response to them, as in the nervous system of animals, have been demonstrated, although these organisms have no nerves, but, as Fechner said, function often as if they had nerves. If, now, plants possess a soul in the sense employed by modern psychology, then intimacy with the life of plants would offer the psychologists much support in testing the psychical functions from the standpoint of the unity of all organized beings, and the more exact separation of these psychic functions from other life functions.
I hasten to the close, and must leave unconsidered many important relations of plant physiology to the other sciences. I have not mentioned the studies upon the adaptation of flowers to insects, and vice versa, resulting in fruit production in the former—studies which call into existence a new borderland between zoology and plant physiology. I omitted also to mention the physiological elements in plant geography, also the great assistance which mathematics has rendered our science, and must likewise pass over much besides.
I have been able to trace only in a few characteristic examples the results which issue from a consideration of the relation of plant physiology to the other sciences. Essentially my whole treatment of the subject has been merely an example, for whatever holds true in my specialty holds true likewise in every other branch of knowledge, namely, the very intimate union of each with other, often widely separated, branches of learning—a union which, with the progress of research, assumes constantly greater power.
The relation of the individual branches of science to each other proves to be so complicated, as is clear from the examples cited, that we may well conceive how all attempts must be frustrated which, from Bacon to d'Alembert and from the encyclopedists to the present time, had for their object a classification of the sciences. One can not parcel off the sciences like a building plot. We ourselves have drawn the division lines between the individual sciences, compelled by the limitations of our human mind, which necessitates us to make a division of labor. But with our advances these boundaries disappear; the individual studies, often inimically opposed, unite into a single whole. Thus science ​seems to be one great totality whose parts are in reciprocal relation and mutual interaction, like the organs of a living organism. I would like to consider the unity of science under the figure of a tree of life which grows upward from the earth from which one part takes its power and nutriment and in which it finds its support. The parts of this tree—roots, stem, branches, and whatever they may all be called—appear to us externally different, but within they belong together; they stand among each other continually in helpful interaction. As the organs, so are the tissues adjusted to each other, and not one of the millions of cells in a tree is without purpose, and if each cell does not stand in fast relation to all others, how also need not each single scientific question be related to all others? This can as little destroy the unity of science as the unity of organic structure of a tree can be destroyed by the fact that each cell does not stand in mutual relation with every other cell.
Wonderingly we see this tree of science develop and broaden out; but for this provision is made, namely, that this tree shall not grow even into the heavens.
After thousands of years of seeking and groping, mankind has finally discovered how he may reach high aims of knowledge in spite of the limitations of his mind, by the often slow and heavily progressing inductive method, and the principle of the division of labor, which first leads to division, but after a rich harvest binds all together. It becomes even clearer that the synthetical mental work, flowing out of the principle of division of labor, must lead to even greater conceptions, and that the number of men must be even greater who, raising themselves above the level of specialists, will be investigators in the best sense of the word.
Held in bounds by the exact nature of its work, science strides forward, ever attaining more and more of what is seemingly unattainable to the human mind, and likewise ever more clearly recognizing the unattainable as unattainable. Indeed, more and more we come face to face with the limits of our knowledge. To the Grecian thinkers it seemed a play that allowed the living to spring out of the lifeless, plants or animals from slime or damp earth. But the inductive method has led us thus far to know that, so far as observation can go, the living can arise only from the living. Even the smallest known living beings, the bacteria, do not come into being parentless, as not long since the last notes of retreat of the defense of spontaneous generation declared. In the organism itself, all that is living proceeds only out of the living—the cell from a cell, the nucleus from a nucleus—and the smallest plastid lying on the very border of microscopic observation proceeds from its like. The possibility enlarged upon by many naturalists, that in the organism living constituents can arise spontaneously, is only a reaction of the old doctrine of spontaneous generation; for, so far as investigation shows, there can rise within the organism organized substance ​only out of the organized. So that growth of organisms appears to us only a multiplication of what is already at hand.
The progress of research has reduced to naught all the facts that pointed toward spontaneous generation, and so we find ourselves duly forced to turn away from spontaneous generation and to regard the living substance as given, just as the physicist regards matter, and takes no further thought as to the question of its origin. The most exact research, even in the domain of matter, has led to impassable boundaries, and the old riddles of the world and all its beings remain unsolved in spite of all progress, and we know, perhaps more clearly than the thinkers of earlier science epochs, that their solution lies beyond the power of the human mind. They remain as unsolvable to the greatest philosopher as well as to the simplest understanding. Other faculties of the mind than those busied in the sober pursuit of science may undertake to show a tangible relation between eternity and our own insignificance.
The mind of the most learned, free from the shadow of its own greatness, bows with the spirit of a child before the unknowable, before that source of all Being which the greatest German poet has thus designated:
" * * * der sich selbst erschuf Von Ewigkeit in schaffendem Beruf, * * * der den Glauben schafft Vertrauen, Liebe, Thätigkeit und Kraft."
* ↑ Inaugural address delivered on the 24th of October, 1898, in the festival hall of the University of Vienna. Translated from the original German, published at Vienna, 1898.
* ↑ According to Buhse the peach tree grows wild in the Persian province of Ghilan.
* ↑ Certain varieties of "kohl" (cabbage) (e.g., the varviol) are called in lower Austrian dialect "kauli," which corresponds more nearly to the Latin stem.