INFLUENCE OF WATER 15 



plant life. The greater part of this per cent, enters the 

 plants through the roots. 



The 75% to 90% of water making the fresh substance 

 of plants is water in plant composition, and can only be 

 taken from the plants by excessive heat. However, 

 this water in composition is dependent upon the 

 amount of moisture contained in the soil and the humid- 

 ity of the atmosphere because the growth of the plant is 

 retarded or advanced as the amount of moisture in the 

 soil is available. This moisture in turn is controlled 

 more by the soil than the atmospheric temperature. 

 Hence, it is necessary to have moisture in the ground in 

 the right proportion for regulating the heat to retard the 

 process of evaporation as well as to promote the develop- 

 ment of plant food. 



It is impossible to definitely define what amount of 

 moisture is required for the growth of a plant because a 

 great many conditions enter. A crop may require 300 

 tons of water for growth to maturity. It may be nec- 

 essary for the soil to furnish 350 tons on account of 

 varying conditions. Some the farmer can control, 

 others he cannot. Water that must be supplied for the 

 growing crops includes that which is constantly evapor- 

 ating from the ground and also that which the leaf and 

 stem of the plant are giving off. 



The amount of plant food in water is very small; that 

 is, the solution is in a very diluted form. For this 

 reason a plant consumes many times its weight in water 

 to get the necessary food. 



The principal factor which determines the water 

 requirements of a plant is the humidity of the atmos- 

 phere. In climates where the atmosphere is moist the 

 water requirements for the plants are much less than 



