ENERGY OF PLANTS. The plant body takes up into itself during its life a certain amount of material which for it time forms part of the body and then leaves it. Another portion forms permanently a part of the body, only returning to the inorganic world upon the dissolution of the organism. Likewise the body is constantly receiving energy from without, and losing it again.
(1) The plant receives, with all the material absorbed, a varying amount of potential energy; on the other hand, it loses some energy by reason of the separation from its body of gases, liquids, and solids, as in the eliminated oxygen and car bon dioxide in the water lost by evaporation, and in the seeds, spores, fruit, leaves, etc., that are east off. (2) The radiant energy absorbed or lost in the form of heat, light, and electricity is of vital importance.
Heat is absorbed from and radiated to the sur rounding medium continually, and many plants receive a large amount directly from the sun. About SO per cent. of the light falling upon a leaf is converted into the slower waves of heat. Most of this is dissipated in evaporation of water, which probably prevents death from over heating, since leaves whose transpiration is pre vented become so hot as to die in a short time.
Heat appears to be the only external source of energy for fungi. One of the most important sources of energy for green plants is light. Cer tain wavelengths arc absorbed by chlorophyll (q.v.) to form carbohydrate foods. (See Pnoro sysrruEsts.) Direct sunlight, diffuse light, and artificial light are effective in proportion to their intensity. Only in rare cases is energy in the form of light lost from plants. Certain bae teria, fungi, and other plants emit, under favor able conditions, a greenish-yello• light, the energy for which is apparently released in con !m•tion with respiration. Little is known of the relation of electric energy to plant life; direct observations show that there are differences of potential in various organs of a living plant amounting to one4enth of a volt or more, but the explanation of this difference is still un known. Apparently of electric energy is indicated by the disturbance of electric poten tial in excited motor organs. in which a general similarity to the muscle-nerve discharge in ani mals may be detected. See AIOTon °ROANS.