WATER REQUIRED BY CROPS 53 



i 



required 2,62, 310, 393, and 774 parts of water to produce 



one part of dry matter. 



TABLE V 



WATER EVAPORATED BY GROWING PLANTS FOR ONE PART 

 OF DRY MATTER PRODUCED 



Results obtained by 



Two circumstances seem especially to influence the relation 

 of water supply to produce i . The amount of water supplied ; 

 2. Its richness or poverty in plant food. These two circum- 

 stances are naturally connected. When the soil contains little 

 water, the solution in the soil is of a comparatively con- 

 centrated character. When much rain has fallen, the supply 

 of water in the soil may be ample, but it usually contains 

 very little plant food. The evaporating organs of the plant are 

 constructed so as to act to the greatest advantage under both 

 circumstances. When much water enters the plant, the cells 

 controlling the stomata in the leaves become turgid, and their 

 swelling determines the opening of the stomata as widely as 

 possible, thus increasing the evaporation. When, on the other 

 hand, the supply of water falls short, the cells in question 

 shrink, the stomata are closed, and evaporation is diminished. 



