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 - 

 Clearing 

 plants 



Disintegration 



by saprophytes 

 parasites 



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 



