BOTANY, the natural history of the vegetable kingdom, the science that treats of plants. It forms, with zoology, the subject of biology in its more comprehensive sense. Plants are living beings which derive their chief sustenance on the one hand from water, which, together with certain dissolved mineral substances, they take in through their roots from the soil, and on the other from carbonic acid gas, which they absorb through their leaves from the atmosphere. Plants alone are able thus to unite inorganic materials and create from them organic compounds capable of sustaining life. Plants thus have, in the economy of nature, the important function of forming from the crude substances of the mineral kingdom the elaborated food materials necessary, not only for their own vital energies, but for the direct or indirect support of all animal life as well. The process by which plants accomplish this chemical change is called assimilation and is carried on only through the agency of light and in the presence of their peculiar green pigment, known as leaf green or chlorophyll. The first product of the process (which is chemically one of deoxidation) is starch. Nitrogen, sodium, sulphur, and a few other elements are taken in by plants through their roots and in the form of dilute solutions. These elements combine with the starch derived by assimilation and form protoplasm and the other highly complex substances of the plant.
All plants, like animals, are composed of small bodies, which at least in their early stages, are microscopic masses of protoplasm, each provided with a specialized portion known as a nucleus. These bodies are called cells, although the name is inappropriate and founded upon the crude and mistaken ideas of the earliest microscopists. Plant cells differ from animal cells in the fact that they are not naked, but are each enveloped in a peculiar, usually transparent membrane of cellulose, a tough, elastic substance in composition allied to starch. In the simplest plants, it is often called protophytes. The cells are solitary, few, or, if more numerous, are essentially alike, being grouped usually in gelatinous masses. In the higher plants, however, the cells are always very numerous and many of them undergo great changes, some being transformed to tubes or vessels for the transmission of the sap, others being elongated and hardened into woody fibers, serve to give strength to the plant body, while still others, such as those of the outer layer (epidermis) assume a protective function.
Botany may be divided into three chief branches.
Structural Botany.—Structural botany includes all inquiries into the form, arrangement, internal anatomy, and composition of plants and their members.
Physiological Botany.—Physiological botany treats of the vital processes of the plant, both physical and chemical.
Systematic Botany.—Systematic botany deals with the different kinds of plants and groups them according to their racial affinities into orders, families, genera, species, varieties, and forms. Botanical histology is a term commonly applied to the minute anatomy or microscopic structure of the plants, especially of their tissues. Cytology deals with the physiology and histology of the individual cells. Vegetable pathology is a branch of physiology treating of plant diseases. Ecology comprehends a recently developed and highly interesting examination of the relations which exist between the structure of the plant and its environment. Economic botany treats of the uses of plants and has its application in agriculture, horticulture, forestry, pharmacy, and medicine.
Plants may be divided into (1) those which are reproduced by means of minute one-celled bodies, destitute of an embryo, and called spores; and (2) those which are propagated by multicellular seeds containing each a latent and extremely rudimentary plantlet, the embryo. Plants of the former class have long been known as cryptogams or flowerless plants, the term sporophytes being preferred by many critical writers. The cryptogams include the following groups: Fungi (molds, mildews, rusts, smuts, toadstools and mushrooms); algæ (sea weeds, diatoms, desmids, etc.); lichens, scale mosses, or liverworts, true mosses, ferns, and fern allies (club mosses, horse tails, or scouring rushes, etc.). The fungi, algæ, and lichens are grouped together under the name thallophytes and the scale mosses and true mosses under the name of bryophytes, while the ferns and their allies are often called pteridophytes. Fungi differ from algae in the uniform lack of chlorophyll or green coloring matter. Lichens, the scale-like incrustations, usually of a gray or brown color, found upon rocks, tree trunks, etc., are composite beings, including green cells like those of algae, but surrounded by fine, usually colorless, filaments like a fungus.
Bryophytes.—The most striking feature of the bryophytes (mosses) and pteridophytes (ferns) is a strongly developed alternation of generations. Thus, in a fern, the spores, after falling to the ground, do not produce directly another plant like the one which bore them, but give rise to a minute plantlet, often heart-shaped, known as a prothallium. Upon this are borne the antheridia, or male organs, and archegonia, or female organs. Fertilization is accomplished by motile antherozoids, developed in the antheridia.
Flowering Plants.—The other great division of the vegetable kingdom comprises the phanerogams or flowering plants. From the fact that they produce true seeds, they are technically known as spermatophytes. Flowering plants include all our ordinary trees and shrubs of temperate climates as well as most of the herbaceous vegetation growing upon the land. In a complete or highly developed flower there are four series of parts. The outermost, which is also the lowest on the stem, is the calyx. It is usually more or less cup-shaped and commonly green. If it is divided to the base, its parts are known as sepals. Its function is, in general, protective. It shields the innermore delicate parts of the flower, especially in the early and tender stages, against injury from the weather, destructive insects, etc. The next series of floral members is the corolla, which is usually showy and of a color other than green. Its function is, in part, protective, but its bright coloration, as well as its peculiar forms, has undoubtedly been developed to attract and facilitate the visits of insects for the fertilizing of the flower. The corolla may consist of a cup or tube or may be made up of separate parts, the petals.
Interior to the petals are the stamens. These consist of a thread-like stalk portion, the filament, and a usually two-celled sac, the anther. In the cells of the anther is the dustlike pollen. At the center of the flower stands the pistil. This may consist of a simple, highly modified leaf, or may be composed of several such members, the carpels, more or less completely fused together. When fully developed, the pistil has three parts, a basal sac, the ovary, surmounted by a short or long columnar portion, the style, which in its turn, bears at or near its usually enlarged summit, a soft, often viscid area, the stigma, for the reception of the pollen. In the ovary are one or more globose or oval bodies, the ovules, which, after fertilization by the pollen, become seeds. These ovules are borne upon the incurved edges of the carpels, although this fact is often very obscure. The pistil and stamens are the essential parts of the flower, while the calyx and corolla, one or both of which may be wholly lacking, are accessory parts. When stamens and pistil are found in the same flower, it is said to be perfect. When they occur in different flowers upon the same individual, the plant is said to be monoecious, while a species in which stamens are borne in the flowers of one individual and the pistils in the flowers of another is dioecious.
In order that a flower may perfect seeds, it is (with certain rare exceptions) necessary that the pollen grains be transferred from the anthers to the stigma. This transfer, pollenation, is sometimes effected by a contrivance or movement within the flower itself. External agents, however, are often necessary. These are chiefly wind, currents of water, or insects.
Flowering plants are primarily divided into the gymnosperms (sago palms, pines, firs, larch, juniper, gingko, etc.), which have no closed ovary, and the angiosperms, in which the seeds are inclosed in a sac-like ovary. The latter group is again divided into two great sections according to the number of rudimentary leaves in the embryo. The monocotyledons, which have only one seed leaf or cotyledon, include the grasses, sedges, rushes, cat tails, palms, lilies, orchids, etc. These plants usually have leaves with parallel veins and flowers built upon the plan of three. They are also called endogens from the fact that the growth of their stems in thickness is effected not by the addition of external layers, but by the expansion and increased complexity of their internal tissues. The angiosperms, with two seed leaves, are the dicotyledons or exogens, having usually net-veined leaves, and flowers more often upon the plan of five. Exogens include the willows, oaks, elms, pinks, buttercups, mustards, roses, beans, violets, asters, etc.
Classification.—The more noteworthy ancient writers upon plants were Hippocrates (460-357 B. C.), Theophrastus (372-287 B. C.), Pliny (23-79 A. D.), and Dioscorides of the 2d century. The 14th to the 17th centuries produced many botanists of a type known as herbalists, whose often ponderous works contain crude complications of the known sorts of plants, with hints of their uses. During this period the idea of genera among plants was evolved with greater and greater clearness. Linnæus was the first to give to each kind of plant known to him a double designation, consisting of a generic name followed by a specific name, thus: Rosa lucida, Viola pedata, Claytonia Virginiana, Claytonia Caroliniana.
The arrangement of families most generally followed during the 19th century has been that developed by the Genoese botanist, Auguste Gyrame De Candolle, and his son, Alphonse De Candolle. The De Candollean system received its most perfect exposition in the “Genera Plantarum” of the two English botanists, George Bentham (nephew of Jeremy Bentham, the philosopher) and Sir Joseph Dalton Hooker, and was followed in all the systematic writings of Prof. Asa Gray. This system, while undoubtedly possessing great merit in its details, unhappily fails to coincide with what is believed to be the historic sequence in which the different families have been evolved during past geological ages. It is, for this reason, rapidly giving place to a more philosophic system, elaborated by the German botanist, A. W. Eichler (1839-1887) and subsequently developed with great perfection in an extended work upon the “Natural Families of Plants” prepared under the editorship of Professors Engler and Prantl. The system, embracing all plants, begins with the simplest cryptogams and ends with the compositæ, the great family, to which belong the golden rod, aster, thistle, and dandelion.
The subject of vegetable physiology, although dating its beginnings from the observations of Stephen Hales (1677-1761) upon the movement and pressure of sap, made but little advance before 1850. It was from that time greatly stimulated by the acute observation and close reasoning of Charles Darwin in England, and Prof. Julius von Sachs in Germany. Subsequent leaders in this line of investigation have been W. Pfeffer and Edward Strasburger. Anatomical botany is greatly indebted to Anton de Bary. The most meritorious works upon botanical geography, a subject which treats of floral conditions and the distribution of the plants in different countries, have been those of A. H. R. Grisebach, Adolph Engler, and A. F. W. Schimper.
The rapid growth of agricultural colleges in this country, fostered by Government and State aid, has given a great impulse to the study of botany. That branch of it which concerns itself with the diseases of plants, called pathology, has been carried to a point of efficiency not yet reached in any other country. The methods of American botanists have caused systematic botany or taxonomic botany to register great advances during the two decades of the present century. There is now under way a complete revision of North American flora in the light of the geographic relationships of plants. Future progress is likely to be based on the principles of heredity in plants and the correlation of plant functions with plant structure.