SOIL MOISTURE AND DRY FARMING 93 



Plants in the process of growth take up water from 

 the soil by means of minute root hairs at the extremities 

 of the rootlets. The water thus taken into the plant con- 

 tains more or less of certain elements of plant food 

 taken from the soil. It passes from cell to cell or up 

 through tubes within the plant until it reaches the leaves, 

 whence it passes off into the air. Through the medium 

 of water, therefore, the elements concerned in promot- 

 ing growth are distributed to all parts of the plant. As 

 the water passes off into the air, there is a demand for 

 more water, to sustain the processes of growth, hence 

 the demand upon the water supply in the soil continues 

 until growth is completed. 



Many things are yet to be learned about the tran- 

 spiration of water through plants. It would seem safe to 

 say, however, that it is influenced by the following con- 

 ditions: It is increased: (1) by increased temperature; 

 (2) by decreased humidity; (3) by increase in the 

 velocity of the wind; (4) by increase in the sunlight; (5) 

 by increasing age in the plant up to the blossoming 

 stage, and (6) by increase in the strength and the diffu- 

 sion of the root system. It is very evident, therefore, 

 that transpiration from plants is more rapid, other things 

 being equal, in dry than in humid climates. It is de- 

 creased: (1) by increase in the soil water of the food 

 elements which the plants require to properly sustain 

 them, and (2) by adaptation in the plants to the require- 

 ments of growth under dry conditions. This last con- 

 sideration is one of great moment, viewed from the 

 standpoint of the future of dry farming. 



The farmer can do but little directly to reduce tran- 

 spiration in the crops. The greater the supply of plant 

 food maintained in the soil, and the more available its 

 condition, the less will be the relative amount of water 

 taken from the soil. This emphasizes the wisdom on 

 the part of the dry land farmer in maintaining a liberal 



