70 THE VEGETATIVE FUNCTIONS OF PLANTS 



of chemistry, organic chemistry, is devoted to a study of 

 organic substances, all of which are compounds of carbon. 

 Inorganic chemistry is concerned with all other substances. 

 68. Nutrition of Plants and Animals. The foods of 

 every living thing those substances which, by digestion 

 and assimilation, can be incorporated into the structure 



Animals 



Chlorophyll- 

 tearing 

 plants 



Disintegration 



by saprophyte B 



& parasites 



Inorganic 



matter 



(Chemical 



elements and 



compounds) 



FIG. 52. The organic cycle 



of the living body as a part of it are all organic. In this 

 respect animals and plants are alike; they both require 

 organic substances as food. Thus it is evident that there 

 must be a continual formation of organic compounds out 

 of inorganic in order to maintain the food supply of the 

 world. As we shall soon learn, this is the great and funda- 

 mental role of green plants in the world's economy to 

 elaborate organic compounds for food out of inorganic 



