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 com prehensive sense. Plants are living be ings which derive their chief sustenance on the one hand from water, which, to gether with certain dissolved mineral substances, they take in through their roots from the soil, and on the other from carbonic acid gas, which they ab sorb through their leaves from the at mosphere. 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 sub stances 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 ani mal 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 pig ment, known as leaf green or chloro phyll. 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 ele ments 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 spe cialized 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 envel oped 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 gelatin ous masses. In the higher plants, how ever, the cells are always very numer ous and many of them undergo great changes, some being transformed to tubes or vessels for the transmission of the sap, others being elongated and har dened 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 func tion.
Botany may be divided into three chief branches.
Structural Botany.—Structural botany includes all inquiries into the form, ar rangement, internal anatomy, and com position of plants and their members.
Physiological Botany. — Physiological botany treats of the vital processes of the plant, both physical and chemical.
Systematic Botany.—Systematic bot any 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 micro scopic 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 devel oped and highly interesting examination of the relations which exist between the structure of the plant and its environ ment. Economic botany treats of the uses of plants and has its application in agriculture, horticulture, forestry, phar macy, 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) ; algm (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, algm, 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 alga in the uniform lack of chlorophyll or green coloring matter. Lichens, the scale-like incrusta tions, usually of a gray or brown color, found upon rocks, tree trunks, etc., are composite beings, including green cells like those of algm, but surrounded by fine, usually colorless, filaments like a fungus.