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 filing 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 aërial 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 aërial 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.