40 AGRICULTURE 



the air by the leaf. The carbon is retained for food. But it is 

 not used in its pure form. It is united with the oxygen and hydro- 

 gen of the sap to make starch and sugar. These substances form 

 plant food. All parts of the plant stem, branches, leaves, and 

 root are nourished by food formed in the leaf laboratory from 

 elements gathered from the soil and the air. 



Need of Sunlight. The two processes, the formation of chlo- 

 rophyl and the changing of carbon, oxygen, and hydrogen into 

 starch and sugar, cannot take place without sunlight. The plant 

 is like a machine run by a motor, the sun. All parts of the machine 

 may be perfect and in readiness, but their work does not proceed 

 unless the motor is in action. 



Need of Water. Leaves perform other work besides taking 

 ^^^^^^^^ in and preparing food. It 

 requires a great deal more 

 IB water to carry food from 



753 POUNDS 



OATS i.aoe POUNDS 



the roots to the leaves than 

 is needed by the plant in its 

 growth. The surplus water 

 is transpired, or given out, 



Amount of water used in producing one pound of r ^ leaves and SO re- 

 _ dry matter " 



turned to the air. Experi- 

 ments prove that a plant uses several hundred pounds of water in 

 forming one pound of dry matter. 



Most plants thrive best when they have much sunshine and fre- 

 quent showers. In wet seasons, they suffer for want of sunlight ; 

 in dry ones, they lack water. The cotton plant is a native of the 

 tropics, and it loves warmth and sunshine. It does not thrive in 

 cold, wet weather. 



Sap. The food prepared in the leaves goes to all parts of the 

 cotton plant. It passes through the soft, fibrous layer called the 



