Popular Science Monthly/Volume 51/September 1897/The Scope of Botany
|THE SCOPE OF BOTANY.|
ASSISTANT PROFESSOR OF BOTANY AND VEGETABLE PHYSIOLOGY, LELAND STANFORD JUNIOR UNIVERSITY.
WE hear much talk nowadays about the new chemistry, the new psychology, the new theology, even the new woman. It is not my purpose to present in this paper any remarks which could be styled "the new botany," for I hope that there is no new botany. Every department of human inquiry should be plastic enough to be modified by increasing knowledge, it should open new fields for investigation, and its members should increase in power. I feel that botany has been plastic, that the science has grown through the years until now it has not merely men who are actively seeking its development, but also those who are seeking for knowledge in ways and by means that have never before been employed, seeking for a knowledge not of facts only—interesting as many of these may be in themselves—but seeking in these facts, painfully and slowly accumulated, the evidences of deeper things, of the great principles which govern the world. The definition is a familiar one—"botany is that science which seeks to answer every reasonable question regarding plants"—and to many people botany is nothing more; but I should not venture to write upon this topic had I nothing more to say than this. The botanist regards his plants not as an end, but as a means of learning a little more about life. The human physiologist was the first to try to penetrate the mystery of life; later the animal physiologist, studying lower forms than man, attacked the same problem; and still later, only within the last hundred years one may say, the vegetable physiologist has come to the aid of the other two. All three, studying the manifestations of life, are seeking to solve the puzzle. What is life itself? With such an aim, the science of botany is more than a pleasant recreation for a summer holiday, it is more than a little accomplishment which can be taught in a finishing school for girls, it is even more than the sentimental or the poetic or the artistic contemplation of the beautiful as displayed in the rose and the lily. The botanist is devoting his time, his energy, his ability (if he has any) to the study of plants not because "it must be so lovely to be always studying flowers," as I have heard so often to my great discomfort, but that he may learn something that will help his fellows in their everyday lives, give them some truer notion of the physical life, and reveal to them some of the principles that underlie it all.
This sounds very fine, but how is the botanist doing all this;and what is the evidence that he has even begun to do some of this? The beginning of botany in this country, so far as the white settlers are concerned, was coincident with the first exploring expeditions, when the hardy pioneers made note of the vegetation, whether it was luxuriant or sparse, whether the plants were poisonous, useless, or useful. That even then a better and more general knowledge of the flora was deemed important, is proved by the record that at the college at Newtowne, founded in 1636 and now known as Harvard University, the study of plants was part of the curriculum in every summer term. To learn the names and the striking properties, useful or harmful, of the plants of a new country is the most natural endeavor of those who are to make it their home. From that time until now, it has been the custom to teach in the schools, and in many of the colleges, just these things. Because most of us go no further in our study of plants, we conclude that this must be all. The school boy and girl painfully learn the descriptive nomenclature, as we find it set forth with wonderful clearness in Gray's Text-book of Botany—that leaves are linear or obcordate or punctate with pellucid dots; that stamens are distinct or hypogynous or tetradynamous; and then they find that the bird-foot violet is technically known as Viola pedata and the lily of the valley Convallaria majalis. But the school boy and girl have thus simply acquired one means of learning more of Nature. Botany is not a science of names, a science overloaded with names though it may be. The individual who destroys a flower by tearing it to pieces (analyzes it, as the ladies say), and finds by the aid of some tiresome artificial key the Latin name of the plant which bears it, has conquered the difficulties of the botanical alphabet; but until he goes further he knows absolutely nothing of the literature of Nature. Children now learn to read before they learn the alphabet, and in many of our better schools the pupils begin to study plants before they learn the descriptive terms applied to them. To have a knowledge merely of the names of plants is to possess a series of jug-handles without the jugs or anything in them. The handles belong with the jugs, and jugs should have, at times at least, something in them. Now, the truly scientific man who seems to be devoting his time to acquiring a knowledge of the names of plants, is in reality learning much more about them. He sees that plants of different sorts resemble one another in greater and less degrees. Those which resemble one another, not merely in superficial characters, which may be due merely to like conditions of growth and life, but in the more fundamental and less obvious characters, he assumes are related; and his studies lead him to formulate a classification which shall indicate in what ways and in what degrees the different plants are related. So we see the first step in the development of botany, the study of plants with a view to arranging them in some classification which shall subserve the convenience of students and at the same time indicate the relationships of plants to one another. But the word relationship implies something more than superficial resemblance. The resemblance is an index of descent. The older botanists—Jussieu, Linnæus, and others like them—believed that plants are now as they were created created either at the beginning of the world or brought into existence later by separate acts of creation. The more critical observations of later years have shown that no two plants are exactly alike, that the offspring are not the duplicates of the parents, that plants are constantly changing as organisms and as generations of organisms. Certain influences cause certain changes; the different conditions to which plants are exposed in sunny and shaded, in moist and dry, in exposed and sheltered positions—the climatic, the geological, the geographical conditions—all have their effects. And so the study of plants extends from the examination of those just about us to a comparison of these familiar forms with those in other localities. There develops the science of geographical botany, which seeks to penetrate the reasons for the existence of certain plants as characterizing the North American, the central European, the Australian, and other floras.
In order to solve the problems thus encountered, the botanist must know not merely the present geographical and geological conditions of our globe, or of that part of it which he especially studies, but also what its geological history has been. This throws light upon many questions. For example, the North American flora is much richer than that of Europe. We gain some idea as to the reasons for this when we realize that the last ice period made much of Europe and of North America uninhabitable, as well for plants as for animals. All were compelled to migrate to the southward or to perish. The Isthmus of Panama and the broad expanse of Central America offered a refuge for the tender forms which could not withstand the rigors of the Ice Age when North America was covered to the Ohio Valley with a great continental glacier. In the milder climes many of them survived, and as the ice retreated they slowly followed it—how, I shall take occasion to show in a moment. But between the ice-bound continent of Europe and the warmer lands to the southward intervened then as now the broad expanse of the Mediterranean, which could be traversed but by few animals and by still fewer plants. Many forms perished, and their places are empty to this day. Hence we see one reason for the greater number of plant species on our own continent.
The botanical geologist finds other things to study, for there are many plants of bygone ages preserved to this day as fossils in the rocks of various horizons. The science of paleobotany grows more slowly than the science of paleozoölogy, which greedily usurps the name of paleontology, as if plants were not quite as important, had not contributed quite as much of value to the earth's crust, as animals. The reasons why paleobotany is such a slow-growing and fragmentary science are two. In the first place, as I have suggested, paleontologists devote themselves in their investigations and teaching too exclusively to animal remains, and hence he who will know more of the plants of past ages must study and learn largely unaided. But the second reason is more fundamental—namely, that plant structures are less easily preserved than those of animals (whose shells or other hard parts are very resistant), and hence many have been destroyed during the various changes that the rocks in which their remains were imbedded have undergone. The fossil remains which are now known give confirmation of the fact mentioned a moment ago that plants are ever changing. The plants of the Carboniferous Age were very different from those of to-day. The aspect of field and forest then must have been mysterious indeed; the heavy atmosphere, the intense light, the moisture, contributing to a vegetation of more than tropical luxuriance. Between the lofty stems of tree ferns, in the deep shade cast by their great fronds, wandered animals hideous to the eye, though perhaps no more dangerous than our mild-eyed cows. But we find to-day, growing here and there, plants which greatly resemble those of the coal measures, not only the ferns, but the horsetails (scouring rushes of our ancestors, Equisetum), the Lycopodiums, without which no northern Christmas festival is quite complete, and others less conspicuous. These the paleontologist convinces us are the direct descendants of those plants which compose our coal. He thereby adds his facts to that history of life which shows that plants are related, that they have common ancestors, that they have developed through the ages until now.
Another field of botanical study is being cultivated by those who devote themselves to the investigation of the adaptations of plants to their surroundings. The adaptations are so many and so perfect that all are tempted (and many yield) to let their sentimental imaginations replace that spirit of critical inquiry without which no scientific work of lasting value can be done. The adaptations for disseminating seed—the winged fruits of our maples, elms, and lindens, for example, or the silken parachutes of the dandelion and the milkweed, the explosive touch-me-not, and the wild crane's-bill with its boomerang—show one how a region devastated by glaciers, fires, or floods can be repopulated. The relations of flowers to the insects which are tothem were first discovered by Christian Conrad Sprengel, and described in a now rare and highly prized book. The Secret of Nature Revealed; but botanists left Sprengel and his secret to themselves. Darwin rediscovered the secret, then discovered the book, and since then the world has been deluged with writings good and bad on this most fascinating subject. The whole field of phytobiology, the adaptations of plants to their surroundings, is open to every one whose interest in Nature takes him into the fields and woods—even into the public parks. No knowledge of technical terms is necessary to enable one to pull apart one of the great horse-chest-nut buds, to notice the water-proofing varnish on the outside, the scale armor just within, the soft, downy padding which protects the minute leaves and the tip of the stem from sudden changes of temperature, to see that leaves or flower cluster are already formed in miniature ready to burst their coverings when the favorable time shall come.
The minute internal structure of the plant is as important a subject for investigation as the more evident features of which I have just spoken. The microscopic study of plants leads one to the most fundamental questions in biological science. It was in consequence of the microscopic studies of a botanist that it was discovered that all organisms are composed of cells, that these cells are essentially minute masses of a viscid substance—protoplasm which—is "the physical basis of life." Is it any wonder, then, that men have devoted their lives to its study, seeking through a knowledge of its structure to learn something of the life of which it is the physical, tangible embodiment?
Among plants as among animals there are two modes of reproduction, the sexual and the nonsexual. Higher animals reproduce themselves only sexually. Some of the higher plants reproduce themselves in the wild state nonsexually as well as sexually, as, for example, the blackberry by its runners, the poplar by those saplings which develop from underground parts often quite distant from the parent trunk; and most of the higher plants can be reproduced in cultivation by cuttings, slips, etc. The sexual reproduction has been developed from simple forms in low plants—for example, the seaweeds—to a state of complexity among the flowering plants which is equal to that among the higher animals. Though there are no superficial resemblances between the sexual reproduction of animals and that of plants, yet the processes are intrinsically the same. The differences are mainly superficial, like those in the means of conveying the male elements to the female elements. The male and female elements in plants are very different from one another, just as in animals, much more different from one another than these elements are from the corresponding elements among animals. In the one kingdom as in the other fertilization takes place when a male element fuses with a female element. So much alike indeed are the microscopic processes in the two kingdoms that much light has been and still may be thrown upon the great general questions of the influence of parents on offspring, of heredity, of descent, of development, by the microscopic study of the phenomena of fertilization and development among plants. There is, therefore, a science of embryology cultivated by botanists which is of almost equal value to man with the science of embryology cultivated by zoölogists.
The microscopic study of the purely vegetative as distinguished from the reproductive parts of plants reveals certain mechanical principles of structure which engineers are now just beginning to follow in their buildings, especially those constructed of materials which in large masses resemble in physical qualities those microscopic elements of which plant structures are composed. We see that the stems of our native trees and those of the palms and others of warmer climes are really frames consisting of long, slender, light yet strong and elastic beams so joined together that they form a structure capable of supporting great weights in spite of the force of gravitation, and so buttressed at points of branching and where the aerial structures spring from their strong foundations in the soil that they are able to resist the really tremendous strains brought to bear upon them by high winds. These principles of buttressing, of accurate balancing, of avoiding sharp angles by the substitution of curves, of a light, elastic framework of great strength, which are common to all the larger plants, we see employed in those buildings which by reason of height, position, or purpose are exposed to great strains. For example, there is more than a fancied resemblance between the Eiffel Tower and the steel lighthouses of our coasts to the buttressed, spreading bases of our elms.
The study of structure, whether macroscopic or microscopic, leads one naturally to investigate the functions of the parts. The study of functions is physiology, and since we have given up the older notions as to the sacredness, the supernaturalness, of the phenomena of life in favor of the more rational view that they are chemical and physical, all physiologists to-day are pressing forward, with chemistry and physics as their allies, to larger knowledge and clearer ideas as to what constitutes life. Far as we still are from a solution of the riddle of the ages, yet during the present century progress hitherto unequaled has been made. Animal and vegetable physiologists are now going hand in hand toward their common goal. In studying the processes of nutrition, growth, reproduction, and the phenomena of perception, reaction, and exhaustion, they are supplementing one another. There are indeed some few physiologists of training and disposition so broad that they decline to be known as animal or as vegetable physiologists, but wish to be called what they really are, students of the functions of living organisms and seekers after light from whatever source upon life itself. The more one studies the physiology of animals and plants the more one sees that the distinctions which have been made between the two are more apparent than real, and that as in so many other cases our names are for convenience rather than for the exact expression of the truth.
The physiologist finds that there are two great classes of plants: (1) Those which, able to obtain from the crude materials of the soil and the air all the elements which they need for their nutrition, lead self-dependent existences; and (2) those which, unable to elaborate their food from such matters, must get it from other organisms, either directly or indirectly. All animals depend ultimately for their food upon those plants which are able to elaborate living matter from lifeless mineral salts, water, and air. But there are quite as many plants which are as dependent as animals. The groups of parasites, the flowering and the flowerless, the dodders and many of the fungi and bacteria, for example, are absolutely dependent upon living organisms, either animal or vegetable as the case may be, for their food. Other plants extract from the dead and more or less decayed remains of organisms the highly elaborated nitrogenous and carbon compounds which are essential to all life. Still others are fairly independent, but supplement their self-made food by other means; for example, the whole group of insectivorous plants and several of the orchids. The saprophytic plants, those living on dead organic matter, are very important in the economy of Nature. They accomplish rapidly, and with much less damage or offense to other organisms, the decomposition of otherwise waste matters which could be removed, but slowly by the processes of chemical nonvital oxidation. Even the parasites are not wholly evils, for some of these man has already tamed and compelled to perform some of the most important domestic operations—the raising of bread and the making of cheese and vinegar. Alcohol is one product of the activity of yeasts, and to these we owe our wines and beers. The precision in the manufacture and the uniform quality of the product of bread, cheese, vinegar, and beer have come only within recent decades when the microscopic organisms upon which these processes depend have become known and regularly raised like wheat and cattle. Recent investigations plainly suggest that greater precision and more uniform success can be obtained in the production of wines and in the curing of tobaccos. Doubtless we have but begun to domesticate the plant parasites which can be made useful to man, and more extended investigations will probably show that many processes in the domestic and other arts which are now tardy and uncertain can be carried on rapidly and accurately.
The science of bacteriology has now become so specially developed along medical lines that in this aspect it can scarcely be counted longer a part of botany; but we should not forget that the first knowledge of the bacteria came through botanists, and that the methods now employed in studying and combating them were first suggested by botanists, and every teacher of botany should regard it both a duty and a privilege to spread among his pupils and the public in general such a knowledge of the habits and effects of these minute organisms that public sentiment will demand not only personal but municipal cleanliness. An adequate supply of water, free from contamination at its sources and in its passage to our houses, contributes not only to the comfort, but greatly also to the health, of any community. The installation of a system of sewerage, for the safe disposal of the extremely dangerous waste matters of houses and stables, will come as soon as public sentiment is enlightened as to the probability of fatal disease resulting from the infection of drinking water, milk, and other uncooked foods from such decaying matters. It is now known that street dust contains millions of organisms which, when they find lodgment in human bodies, made suitable by weakness for their growth, cause the most malignant maladies. Even the dust of our rooms contains numberless organisms of these same sorts. So it behooves us as intelligent people to strive to bring about such cleanliness of streets and houses that these dangers will be reduced to a minimum.
The bacterial and fungous diseases of other animals than man, and the diseases of plants, are still being studied by botanists. We have only begun to know the dangers which menace the farmers' crops and stock. To study these dangers, to devise means to avoid them, to discover cures for those plants which are attacked by disease, are the tasks which the vegetable pathologist has before him.
Agriculture and horticulture are simply the practical applications of principles defined by the study of vegetable physiology. Questions as to the suitability of certain soils for certain crops are answered by the practical farmer, who scorns the aid which the scientific man might give him, by such expensive experiments as sowing the area in question with the seeds of the crop which he hopes to reap. If the crop is a good one, the farmer rejoices; if he gets but a trifling return for his season's labor, he grumbles at his luck, or wants the Government to order a bounty, or to pass a prohibitory tariff. The market-gardener should know now as the result of the published investigations of vegetable physiologists at agricultural experiment stations, that some of the vegetables and fruits which bring the highest prices when marketed out of season can be brought to perfection much earlier when grown not only in sunlight by day, but under the electric light by night. Lettuce, for example, can be marketed about two weeks sooner after planting if illuminated day and night.
The horticulturist daily proves by producing various and often striking varieties of flowers or fruits the falsity of the old notions as to the fixity of living organisms. I must confess that it seems to me rather disrespectful, some persons might say rather impious, so to tamper with the natural or "divinely appointed" forms of plants, as to produce the monstrous chrysanthemums which we may see in exhibitions or in private houses. But these exaggerated and often extremely ugly because so artificial forms are the strongest evidences that the organic world, of which we are a part, is extremely plastic still in spite of its age; and that those factors which have accomplished the evolution of present complexity from primitive simplicity are still operative, and that man as well as other organisms has not yet reached his final and highest development.
I wish to say one word of that aspect of botanical science which is still but little regarded in our country, but which, if our successors are to have any forests, must receive due and practical notice. I mean the science of forestry. In Germany especially, but in other European countries also, there are forestry schools, where young men receive that scientific and many-sided training which will fit them properly to administer the private and Government wooded lands. It is an interesting fact that, great as is the expense in maintaining these schools and in managing the forests, yet the forests of Germany are one of the most profitable properties of the Government. The railroads pay a trifling interest still, but the forests yield regular and, for Europe, high interest. We must soon acquire, by purchase or otherwise, such control of our still forested areas as will insure their preservation and intelligent use, else the boastful prophecy which I have heard more than once in Germany will come true, that Germany will be exporting wood to America within fifty years! The Forestry Division of the United States Department of Agriculture, and the small forestry associations scattered here and there in the cities, precisely where there can be no forests, are doing all they can to arouse public interest in the matter, and to prevent further reckless deforestizing. But to leave the trees unfelled is not all; to replant where replanting is still possible, to fell the trees that are now of useful size, to thin out that others may attain better proportions, to protect against fires, these are equally important. To do all this well demands intelligence, knowledge, and training. The training of the skilled forester must be largely botanical; for though he must know enough about zoölogy to be able to distinguish and to combat insect and other animal pests, yet he must know the principles of vegetable physiology and pathology. For these he must study under some thoroughly trained botanist. I have attempted to sketch, I fear in very impressionistic fashion, the scope of a science whose value to man is great and personal, which is many-sided, and which is worthy of the devotion and activity of those to whom it is an absorbing interest.