Popular Science Monthly/Volume 56/November 1899/The New Field Botany
|THE NEW FIELD BOTANY.|
By BYRON D. HALSTED, Sc. D.,
OF RUTGERS COLLEGE.
THERE is something novel every day; were it not so this earth would grow monotonous to all, even as it does now to many, and chiefly because such do not have the opportunity or the desire to learn some new thing. Facts unknown before are constantly coming to the light, and principles are being deduced that serve as a stepping stone to other and broader fields of knowledge. So accustomed are we to this that even a new branch of science may dawn upon the horizon without causing a wonder in our minds. In this day of ologies the birth of a new one comes without the formal two-line notice in the daily press, just as old ones pass from view without tear or epitaph.
Phytoecology as a word is not long as scientific-terms go, and the Greek that lies back of it barely suggests the meaning of the term, a fact not at all peculiar to the present instance. Of course, it has to do with plants, and is therefore a branch of botany.
In one sense that which it stands for is not new, and, as usual, the word has come in the wake of the facts and principles it represents, and therefore becomes a convenient term for a branch of knowledge—a handle, so to say—by which that group of ideas may be held up for study and further growth. The word ecology was first employed by Haeckel, a leading light in zoölogy in our day, to designate the environmental side of animal life.
We will not concern ourselves with definitions, but discuss the field that the term is coined to cover, and leave the reader to formulate a short concise statement of its meaning.
Within the last year a new botanical guide book for teachers has been published, of considerable originality and merit, in which the subject-matter is thrown into four groups, and one of these is Ecology. Another text-book for secondary schools is now before us in which ecology is the heading of one of the three parts into which the treatise is divided. The large output of the educational press at the present time along the line in hand suggests that the magazine press should sound the depths of the new branch of science that is pushing its way to the front, or being so pushed by its adherents, and echo the merits of it along the line.
Botany in its stages of growth is interesting historically. It fascinated for a time one of the greatest minds in the modern school, and as a result we have the rich and fruitful history of the science as seen through eyes as great as Julius Sachs's, the master of botany during the last half century. From this work it can be gathered that early in the centuries since the Christian era botany was little more than herborizing—the collecting of specimens, and learning their gross parts, as size of stem and leaf and blossom.
This branch of botany has been cultivated to the present day, and the result is the systematist, with all the refinements of species making and readjustment of genera and orders with the nicety of detail in specific descriptions that only a systematist can fully appreciate.
Later on the study of function was begun, and along with it that of structure; for anatomy and physiology, by whatever terms they may be known, advance hand in hand, because inseparable. One worker may look more to the activities than another who toils with the structural relations and finds these problems enough for a lifetime.
This botany of the dissecting table in contrast with that of the collector and his dried specimens grew apace, taking new leases of life at the uprising of new hypotheses, and long advances with the improvement of implements for work. It was natural that the cell and all that is made from it should invite the inspector to a field of intense interest, somewhat at the expense of the functions of the parts. In short, the field was open, the race was on, and it was a matter of self-restraint that a man did not enter and strive long and well for some anatomical prize. This branch of botany is still alive, and never more so than to-day, when cytology offers many attractive problems for the cytologist. What with his microtome that cuts his imbedded tissue into slices so thin that twenty-five hundred or more are needed to measure an inch in thickness, with his fixing solutions that kill instantly and hold each particle as if frozen in a cake of ice, and his stains and double stains that pick out the specks as the magnet draws iron filling from a bin of bran—with all these and a hundred more aids to the refinement of the art there is no wonder that the cell becomes a center of attraction, beyond the periphery of which the student can scarcely live. In our closing days of the century it may be known whether the blephroblasts arise antipodally, and whether they are a variation of the centrosomes or should be classed by themselves!
One of the general views of phytoecology is that the forms of plants are modified to adapt them to the conditions under which they exist. Thus the size of a plant is greatly modified by the environment. Two grains of corn indistinguishable in themselves and borne by the same cob may be so situated that one grows into a stately stalk with the ear higher than a horse's head, while the other is a dwarf and unproductive. Below ground the conditions are many, and all subject to infinite variation. Thus, the soil may be deep or shallow, the particles small or large, the moisture abundant or scant, and the food elements close at hand or far to seek—all of which will have a marked influence upon the root system, its size, and form.
Coming to the aerial portion, there are all the factors of weather and climate to work singly or in union to affect the above-ground structure of the plant. Temperature varies through wide ranges of heat and cold, scorching and freezing; while humidity or aridity, sunshine or cloudiness, prevailing winds or sudden tornadoes all have an influence in shaping the structure, developing the part, and fashioning the details of form of the aerial portions. Phytoecology deals with all these, and includes the consideration of that struggle for life that plants are constantly waging, for environment determines that the forms best suited to a given set of conditions will survive. This struggle has been going on since the vegetable life of the earth began, and as a result certain prevailing conditions have brought about groups of plants found as a rule only where these conditions prevail. As water is a leading factor in plant growth, a classification is made upon this basis into the plants of the arid regions called xerophytes. The opposite to desert vegetation is that of the fresh ponds and lakes, called hydrophytes. A third group, the halophytes, includes the vegetation of sea or land where there is an excess of various saline substances, the common salt being the leading one. The last group is the mesophytes, which include plants growing in conditions without the extremes accorded to the other three groups.
This somewhat general classification of the conditions of the environment lends much of interest to that form of field botany now under consideration. As the grouping is made chiefly upon the aqueous conditions, it is fair to assume that plants are especially modified to accommodate themselves to this compound. Plants, for example, unless they are aquatics, need to use large quantities of water to carry on the vital functions. Thus the salts from the soil need to rise dissolved in the crude sap to the leaves, and in order that a sufficient current be kept up there is transpiration going on from all thin or soft exposed parts. The leaves are the chief organs where aqueous vapor is being given off, sometimes to the extent of tons of water upon an acre of area in a single day. This evaporation being largely surface action, it is possible for the plant to check this by reducing the surface, and the leaf is coiled or folded. Other plants have through the ages become adapted to the destructive actions of drought and a dry, hot atmosphere, and have only needle-shaped leaves or even no true ones at all, as many of the cacti in the desert lands of the Western plains.
Again, the surface of the plant may become covered with a felt of fine hairs to prevent rapid evaporation, while other plants with ordinary foliage have the acquired power of moving the leaves so that they will expose their surfaces broadside to the sun, or contrariwise the edges only, as heat and light intensity determine.
Phytoecology deals with all those adaptations of structure, and from which permit the plants to take advantage of the habits and wants of animals. If we are studying the vegetation of a bog, and note the adaptation of the hydrophytic plants, the chances are that attention will soon be called to colorations and structures that indicate a more complete and far-reaching adjustment than simply to the conditions of the wet, spongy bog. A plant may be met with having the leaves in the form of flasks or pitchers, and more or less filled with water. These strange leaves are conspicuously purplish, and this adds to their attractiveness. The upper portion may be variegated, resembling a flower and for the same purpose—namely, to attract insects that find within the pitchers a food which is sought at the risk of life. Many of the entrapped creatures never escape, and yield up their life for the support of that of the captor. Again, the mossy bog may glisten in the sun, and thousands of sundew plants with their pink leaves are growing upon the surface. Each leaf is covered with adhesive stalked glands, and insects lured to and caught by them are devoured by this insectivorous vegetation.
In the pools in the same lowland there may be an abundance of the bladderwort, a floating plant with flowers upon long stalks that raise them into the air and sunshine. With the leaves reduced to a mere framework that bears innumerable bladders, water animals of small size are captured in vast numbers and provide a large part of the nourishment required by the highly specialized hydrophyte.
These are but everyday instances of adaptation between plants and animals for the purpose of nutrition, the adjustment of form being more particularly upon the Vegetative side. Zoölogists may be able to show, however, that certain species of animals are adapted to and quite dependent upon the carnivorous plants.
An ecological problem has been worked out along the above line to a larger extent than generally supposed. If we should take the case of ants only in their relation to structural adaptations for them in plants, it would be seen that fully three thousand species of the latter make use of ants for purposes of protection. The large fighting ants of the tropics, when provided with nectar, food, and shelter, will inhabit plants to the partial exclusion of destructive insects and larger foraging animals. Interesting as all this is, it is not the time and place to go into the details of how the ant-fostering plants have their nectar glands upon stems or leaf, rich soft hairs in tufts for food, and homes provided in hollows and chambers. There is still a more intimate association of termites with some of the toadstool-like plants, where the ants foster the fungi and seem to understand some of the essentials of veritable gardening in miniature form.
The most familiar branch of phytoecology, as it concerns adaptations for insect visitations, is that which relates to the production of seed. Floral structures, so wonderfully varied in form and color and withal attractive to every lover of the beautiful, are familiar to all, and it only needs to be said in passing that these infinite forms are for the same end—namely, the union of the seed germs, if they may be so styled, of different and often widely separated blossoms.
Sweetness and beauty are not the invariable rule with insect-visited blossoms, for in the long ages that have elapsed during which these adaptations have come about some plants have established an unwritten agreement between beetles and bugs with unsavory tastes. Thus there are the "carrion flowers," so called because of their fetid odor, designed for the sense organs of carrion insects. The "stink-horn" fungi have their offensive spores distributed by a similar set of carrion carriers.
Water and wind claim a share of the species, but here adaptation to the method of fertilization is as fully realized as when insects participate, and the uselessness of showy petals and fantastic forms is emphasized by their absence.
Coming now to the fruits of plants, it is again seen that plants have adapted their offspring, the seed, to the surrounding conditions, not forgetting the wind, the waves, and the tastes and the exterior of passing animals. The breezes carry up and hurl along the light wing-possessed seeds, and the river and ocean bear these and many others onward to a distant land, while by grappling hooks many kinds cling to the hair of animals, or, provided with a pleasing pulp, are carried willingly by birds and other creatures. In short, the devices for seed dispersion are multitudinous, and they provide a large chapter in that branch of botany now styled phytoecology.
How different is the old field botany from the new! Then there was the collector of plants and classifier of his finds, and an arranger of all he could get by exchange or otherwise. His success was measured by the size of his herbarium and his stock in trade as so many duplicates all taken in bloom, but the time of year, locality, and the various conditions of growth were all unknown.
His implements for work were, first, a can or basket, a plant press, and a manual; and, secondly, a lot of paper, a paste pot, and some way of holding the mounts in packets or pigeonholes.
The eyes grew keen as the hunter scoured the forest and field for some kind of plant he had not already possessed. There was a keen relish in discoveries, and it heightened into ecstasy when the specimen needed to be sent away for a name and was returned with his own Latinized and appended to that of the genus.
This was all well and good so far as it went, but looked at from the present vantage ground there was not so much in it. However, his was an essential step to other things, as much so as that of the census taker.
We need to know the species of plants our fair land possesses, and have them described and named. But when the nine hundred and ninety-nine are known, it is a waste of time to be continually hunting for the thousandth. Look for it, but let it be secondary to that of an actual study of the great majority already known. The older botany was a study of the dried plants in all those details that are laid down in the manuals. It lacked something of the true vitality that is inherent in a biological science, for often the life had gone out before the subject came up for study. To the phytoecologist it was somewhat as the shell without the meat, or the bird's nest of a previous year.
Since those days of our forefathers there has come the minute anatomy of plants, followed closely by physiology; and now with the working knowledge of these two modern branches of botany the student has again taken to the field. He is making the wood-lot his laboratory, and the garden, so to say, his lecture room. He has a fair knowledge of systematic botany, but finds himself rearranging the families and genera to fit the facts determined by his ecological study. If two species of the same genus are widely separated in habitat, he is determining the factors that led to the separation. Why did one smart weed become a climber, another an upright herb, and a third a prostrate creeper, are questions that may not have entered the mind of the plant collector; but now the phytoecologist finds much interest in considering questions of this type. What are the differences between a species inhabiting the water and another of the same genus upon dry land, or what has led one group of the morning-glory family to become parasites and exist as the dodders upon other living plants?
The older botanist held his subject under the best mental illumination of his time, but his physical light, that of a pine knot or a tallow dip, also contrasts strongly with that of the present gas jet and electric arc.
The wonder should be that he saw so well, and all who follow him can not but feel grateful for the path he blazed through the dense forests of ignorance and the bridges he made over the streams of doubt in specific distinctions. It was a noble work, but it is nearly past in the older parts of our country; and while some of that school should linger to readjust their genera, make new combinations of species, and attempt to satisfy the claims of priority, the rank and file will largely leave systematic botany and the herborizing it embraces, and betake themselves to the open fields of phytoecology. It may be along the line of structural adaptations when we will have morphological phytoecology, or the adjustment of function to the environment when there will be physiological phytoecology. These two branches when combined to elucidate problems of relationship between the plant and its surroundings as involved in accommodation in its comprehensive sense there will be phytoecology with climate, geology, geography, or fossils as the leading feature, as the case may be.
In the older botany the plant alone in itself was the subject of study. The newer botany takes the plant in its surroundings and all that its relationships to other plants may suggest as the subject for analysis. In the one case the plant was all and its place of growth accidental, a dried specimen from any unknown habitat was enough; but now the environment and the numerous lines of relationship that reach out from the living plant in situ are the major subjects for study. The former was field botany because the field contained the plant, the latter is field botany in that the plant embraces in its study all else in the field in which it. lives. The one had as its leading question, What is your name and where do you belong in my herbarium? while the other raises an endless list of queries, of which How came you here and when? Why these curious glands and this strange movement or mimicry? are but average samples. Every spot of color, bend of leaf, and shape of fruit raises a question.
The collector of fifty years ago pulled up or cut off a portion of his plant for a specimen, and rarely measured, weighed, and counted anything about it. The phytoecologist to-day watches his subject as it grows, and if removed it is for the purpose of testing its vital functions under varying circumstances of moisture, heat, or sunlight, and exact recording instruments are a part of the equipment for the investigation.
The underlying thought in the seashore school and the tropical laboratory in botany is this of getting nearer to the haunts of the living plant. Forestry schools that have for their class room the wooded mountains and the botanical gardens with their living herbaria are welcome steps toward the same end of phytoecology.
In view of the above facts, and many more that might be mentioned did space permit, the writer has felt that the present incomplete and faulty presentation of the subject of the newer botany should be placed before the great reading public through the medium of a journal that has as its watchword Progress in Education.