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 e 
ft 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 r61e of green plants in the world's economy to 
elaborate organic compounds for food out of inorganic 
