166 DRY-FARMING 



in various arid districts have shown that one and 

 a half to three times more water evaporates from 

 the plant than directly from well-tilled soil. To the 

 present very little has been learned concerning the 

 most effective methods of checking or controlling 

 this continual loss of water. Transpiration, or the 

 evaporation of water from the plants themselves, 

 and the means of controlling this loss, are subjects of 

 the deepest importance to the dry-farmer. 



Absorption 



To understand the methods for reducing trans- 

 piration, as propos(>d in this chapter, it is necessary 

 to review briefly the manner in which plants take 

 water from the soil. The roots are the organs of 

 water absorption. Practically no water is taken into 

 the plants by the stems or leaves, even under condi- 

 tions of heavy rainfall. Such small ciuantities as 

 may enter the plant through the stems and leaves are 

 of very little value in furthering the life and growth 

 of the ]3lant. The roots alone are of real conse- 

 quence in water absorption. All parts of the roots do 

 not possess equal power of taking up soil- water. In 

 the ]:irocess of water absorption the A'ounger roots 

 are most active and effective. Even of the young 

 roots, however, only certain parts are actively en- 

 gaged in water absorption. At the very tips of the 

 young growing roots are numerous fine hairs, shown 



