The New Student's Reference Work/Respiration
Res′pira′tion (in plants) is the process by which most plants set free in their bodies the energy required for doing the work necessary to maintain life and form new parts. It essentially is identical with the respiration of animals. It consists of several separate but related processes: (1) the absorption of oxygen and its union with the protoplasm or with foods by the action of the protoplasm; (2) the decomposition of this unstable substance, resulting finally in the formation of carbon dioxide and water; (3) ridding the body of these waste products. The oxygen is absorbed directly from the water or air by smaller plants, but in the larger it is distributed to the internal tissues by a system of air passages (see Aëration). Through a reverse process the carbon dioxide is got rid of. The chemical details of respiration are not known. It even is uncertain whether it is the living protoplasm or the foods that are oxidized. Neither is it known how the energy is used nor in what form it is set free. Some of it appears as heat, making the body warmer than the surrounding air. But this heat is so quickly lost that it can only be observed when dissipation of it is hindered. In this the plant is like a cold-blooded animal. On account of the carbon dioxide excreted, the plant loses weight, unless supplied with food; thus, if a seed germinate in darkness, after a few weeks the plantlet may have less than half the dry weight of the seed from which it grew.