Page:The New International Encyclopædia 1st ed. v. 03.djvu/391

* BOTANY. 345 BOTANY. the researches of Schleiden and NHgeli. From that time Ihc science of Plant Anatomy (Phyto- tomy. Plant Histolon:^•) has developed enormous- ly, until now the recognized plant-tissues are very numerous, and their origin and relation to one another in position and function are fairly well understood. Anatomy is associated on the one hand with morphology, since the tissues enter into the structure of organs: and on the other hand with physiology, since the nature of the tissues has to do directly with the various functions of the plant. Cytology. In recent years another definite field of botanical research has been developed, which deals exclusively with the problems of the cell, and is called Cytology (q.v.). It is related to anatomy in that it deals with cells, which in their aggregation form the tissues that are the subject of anatomy. At the same time, it studies cells from the standpoint of mor- phology, since it is concerned with cell-organs. their origin and mutual relationships: while it also has its distinct association with physiolo- gy-, inasmuch as the functions of its organs fur- nish the ultimate problem of the cell. It is through eytological investigation that the tech- nique of research with the microscope has been developed so greatly. The discoveries in methods of killing material, in imbedding, sectioning, and staining, have brought to view structures which were invisible to the observers of a few years ago. The principal jjroblems of cytology at present are the structure and activities of protoplasm, the life-history of plastids ( piotoplasmic organs of the cell, (if which chloroplastids, the green color-bodies of leaves, are exani])les). the struc- ture and function of the nucleus (an essential and permanent organ of the living cell), the reduction of chromosomes (bodies which enter into the structure of the nucleus), the origin and development of the achromatic figure (a peculiar spindle-shaped body which appears in connection with a dividing nucleus), the centro- some (a cell-organ supposed to be prominently concerned in the division of the nucleus), the cell-wall, the development of the sex-cells, fertilization, the embryo, and the problem of heredity. PuYsioLOOY'. Nothing was known of the life of plants in the early part of tlic Seventeenth Century except what had been learned through agricultural and horticultural operations. It was in the latter half of the Seventeenth Cen- tury that the science of Plant Physiology was founded, long after the physiological sig- nificance of the different organs of the human body and of most animals was generally known. The history of the gradual discovery of the various functions of plant-organs is long and full of interest. The foundation of all physiology is the direct observation of vital phenomena, and these must be evoked or altered by experi- ment. It is by means of this experimentation that a definite" knowledge of physiological pro- cesses has developed, until now the student of plant physiolog}' is in possession of a vast body of facts. Vital phenomena in plants are essen- tially the same as in animals, but are often simpler; and hence plants frequently furnish the clues for the interpretation of the more oomplex activities of animals. The important general functions of plants, which furnish the subject-matter for physiologi- cal research, are as follows: Absorption of nia- lerjal and of energy from the outside world; transfer of water through the plant-body, by which materials are properly distributed; trans- piration, by means of which water is lost from the plant's surface: nutrition, including photo- synthesis (the manufacture of carbohydrates), digestion (the conversion of foods into soluble form for transfer), and assimilation (the organ- ization of protoplasm from food-material) : se- cretion ; respiration, by means of which energy is liberated for the "activities of the body"; growth: and movement, which incltides irritable responses to many stimuli. For example, in the higher plants the root is an absorbing organ for water and soluble soil substances; in the root, stem, and leaves there are certain sets of vessels along which water and food-materials travel readily; the leaves and the young stem surface are organs for the absorption and evolution of the carbon dioxide and oxygen, they also give off water by evajjoration (transpiration), and are most im- portant organs for the manufacture of carbohy- drate foods. Although these various processes are distributed among the organs of a complex I)lant, they may all go on in a single cell of the simplest plant. Ecology. A phase of plant physiology which has recently come into prominence as an inde- pendent subject is Ecology or CEcologi,- (q.v.), which deals with the mutual relations" between plants and their environment. Certain phases of ecology, such, as pollination, seed-dispersal, protection, symbiosis, have long been studied, and have been called 'plant biologv-'; but the subject as a whole is of very recent organization. Ecol- ogy as at present organized was first presented by Professor Warming, of Copenhagen, in 1S95, and its fullest recent statement is that of Pro- fessor Schimper. in 1808. The subject is yet in a very formative state, and its formulated state- ments must be regarded as largely tentative. Three rather distinct lines of ecological investi- gation have been developed. One deals with the reactions of plants, tissues, and organs to their environment, and may be called physiologic ecology. A second line has to do with the origin, development, and life relations of the plant com- munities known as plant societies, and may bft called physiographic ecology. The third line is a study of the great forest, grass, desert, and other formations of the globe in relation to climate, and juay be called geographic ccologv Various special subjects connected with plants are also organized into distinct fields of work. Pnleohofanii (q.v.) is a study of fossil plants, a subject which has been developing with remark- able rapidity. Bnrteriolofiti is the science which treats of that very peculiar group of plants known as bacteria, whose relationships to the interests of man are often of great importance, and whose life-processes are so peculiar that they demand spe<ial manipulation. Pntlwlnr;)/ is that division of the subject which deals with plant diseases, chiefly fhose inflicted by other plants. It is this subject which has attracted a great deal of attention in connection with the work of agricultural experiment stations. Eco- nomic holnn//. closely allied to agriculture and horticultire. is a growing subject, which deals with plants from the standpoint of their useful- ness to man. Forestry is a special division of