The New Student's Reference Work/Physiology (of plants)
Physiology (of plants), that branch of science which treats of the activities of living beings. These essentially are the same in plants as in animals, but often are simpler. Plant physiology is concerned with the action of the plant body as a whole, the part which each of its organs takes and the ways in which they are adjusted to one another and the external world. (See Ecology.) The work of a particular part or organ is called its function. The important general functions of plants are absorbtion; water transfer; transpiration; nutrition (in the narrower sense) including digestion, photosynthesis and assimilation; secretion; respiration; growth; and movement. (See these topics and Irritability.) In the higher plants the root is an absorbing organ for water, mineral salts and such organic matter as is soluble in water; the root, stem and leaves are furnished with strands of tissues along which water and foods can travel readily; the leaves and the surface of the stem, at least when young, are organs of absorption and evolution of the gases carbon dioxide and oxygen; they also lose water by evaporation; and they are most important as organs for making carbohydrate foods. All these functions, however, may go on in a single cell of one of the simplest plants.