38 THE BOOK OF CORN 



becomes a part of the plant structure. As carbon diox- 

 ide gas is continually given off to the atmosphere by the 

 decomposition of plants, by all forms of combustion 

 and from many other sources, the supply of carbon 

 is unlimited. 



Hydrogen composes a large proportion of the 

 atmosphere. Its function seems to be that of diluting 

 the oxygen. This gaseous element is taken into the 

 plant through the leaf pores and enters largely into the 

 composition of the carbon compounds. As a very large 

 proportion of the air is composed of hydrogen its 

 supply does not concern the farmer. 



Oxygen also exists in the atmosphere as a gas 

 and its supply is inexhaustible. It enters into the com- 

 position of the carbon compounds and is taken into 

 the plants through the leaves. 



Food Supplied Through Root System — All other 

 elements of plant food are supplied- to the plant 

 through the root system from the soil. With one ex- 

 ception they are all supplied to the plant directly from 

 the soil, which acts as a storehouse of plant food. The 

 exception to this rule is nitrogen, which is in part 

 taken from the, atmosphere, where it exists as a gas, 

 through the agency of leguminous plants. Tubercles 

 are formed on the roots of the leguminous plants 

 through the action of certain organisms. In the build- 

 ing of these tubercles, the organisms take the nitrogen 

 directly from the air and work it into the composition 

 of the plants. When the tubercles decay, the nitrogen 

 is left in the soil, where it can be used by succeeding 

 crops. In this way, by the growth of leguminous 

 crops, the store of nitrogen in the soil is increased. 

 For this reason it has become the general practice 

 among corn farmers to so rotate their crops that a 

 leguminous crop, as clover, cowpeas or soy beans, is 



