NUTRITION. 175 



250. Contrast between respiration and photosyntax. — 



Since the processes of respiration and photosynta.v in green 

 plants are so frecjuently confused, a contrast is here drawn 

 between tlicni. 



RespiraiioJt. Photosynlax. 



Occurs in all living cells. Occurs only in green cells. 

 Indifferent to or retarded by Requires light. 



light. 



Consumes organic matter. Produces organic matter. 



Produces carbon dio.xide. Consumes carbon dioxide. 



Consumes o.vygen. Produces oxygen. 



Sets free energy. Accumulates energy. 



251. Other katabolic changes. — Besides those constitut- 

 ing respiration, a considerable number of other katabolic 

 changes occurr, which are not so closely connected with 

 the vital functions of the jilant. They result in the produc- 

 tion of substances which are of no further use in nutrition 

 and only of incidental \alue for any purpose. Such sub- 

 stances may be stored in some out of the way place, or in 

 such parts as are transient, and Ijy the loss of these parts the 

 useless materials are gotten rid of; or they may be excreted 

 directly. The waste materials are either nitrogenous or 

 non-nitrogenous. 



252. Non-nitrogenous by-products. — ,\mong the non- 

 nitrogenous materials the most important are the carbon 

 acids, such as oxalic, malic, etc., the tannins, the resins, the 

 gums and the volatile oils. These substances are either by- 

 products of photosyntax, or they arise in the course of the 

 assimilation of foods. Oxalic acid is usually gotten rid of by 

 being combined with lime to form calcic oxalate, which 

 crystallizes either in the form of srjuarish crystals or as long 

 needles, the form depending upon the amount of water of 



