7<D FARM DEVELOPMENT 



to spare. The remaining 12 O, oxygen, liberated from 

 the carbon dioxide, is given off, or is sometimes used for 

 some purpose within the plant body. 



This process of making starch can only take place 

 when the plant is exposed to light. While it is not cer- 

 tain that starch is the first product formed in the plant, 

 for the present we may consider it so. We may, there- 

 fore, look upon the chlorophyll bodies as little manufac- 

 tories of starch. To decompose carbon dioxide and to 

 build up starch out of carbon and water, requires energy. 

 This the plant obtains from the sunlight. When the 

 animal consumes the plant, it breaks down these com- 

 pounds and changes part of the carbon back into carbon 

 dioxide and water. The stored-up energy is liberated, 

 and is used by the animal for the production of work or 

 heat or for other bodily functions requiring energy. 



Animals depend on plants. Animals cannot combine 

 the nourishment in the air and soil for use as food. 

 Plants, however, take the food substances available in 

 the air and soil, and by the aid of sunlight build these 

 into compounds useful to animals and man. While only 

 a very small part of the food of plants is obtained from 

 the soil, their growth under ordinary conditions depends 

 directly upon the soil. It is necessary to understand the 

 needs of the plant and the character of the soil so that 

 the land may be handled in the manner best suited to 

 the needs of the crop we wish to grow. The soil is a 

 medium through which the plant obtains water con- 

 taining in solution the mineral and other parts of its food, 

 excepting the CO 2 secured from the air. That the soil 

 is only a medium, is shown by the fact that plants can 

 be grown in pure water, to which is added the necessary 

 nitrogen, phosphoric acid, potash, iron, calcium, etc., 

 required by the plant when grown normally. 



Drainage and cultivation accelerate soil aeration. 

 Drainage, especially tile drainage, where the drains are 



