NUTRITION. 173 



their life processes,. really checks them. They are known as 

 anaerobic plants. 



244. Excretion. — The carbon dioxide produced by res- 

 piration, when not used for photosyntax, is gotten rid of by 

 the reverse of the methods described for the absorption of 

 oxygen. 



245. Release of energy. — The purpose of respiration is 

 to set free energy required for growth and movement. While 

 plants are capable of. utilizing radiant energy of the sun for 

 photosyntax, they must set free within their own bodies the 

 energy requisite for putting in place particles of new material 

 to form new parts, and for the execution of movements, 

 whether internal, such as the streaming or rotation of the 

 protoplasm, or mass movements, such as those of leaves and 

 other members, or movements of locomotion, such as those 

 of swarm pores and sperm cells. (See ^| 276 ff.) The re- 

 quired energy is set free by the decomposition of organic 

 matter. 



246. Loss of weight. — As a consequence there ensues a 

 loss of weight. If a plant, such as a seedling abundantly 

 supplied with reserve food, be compelled to develop in dark- 

 ness, and so allowed to make no additional food, it may be 

 easily demonstrated that a large part, often as much as one 

 half, of its weight will be lost (as gases) in respiration. This 

 loss of weight comes primarily from the decomposition of 

 portions of the living protoplasm. These, however, are soon 

 replaced by the formation of new protoplasm from the pro- 

 teids, and these again are replaced, as already described, by 

 the use of carbohydrates and nitrogenous compounds. Ulti- 

 mately, therefore, respiration results in a diminution of the 

 reserve food, especially of the carbohydrates. 



247. A vital function. — Respiration is a function of the 

 protoplasm, and does not occur simply because oxidizable 

 substances are present in the plant and oxygen is brought 



