WATER OF SOIL IN ITS RELATION TO PLANTS 185 



is not large, however, in comparison with the amount lost 

 by transpiration, although green plants contain from 60 to 

 90 per cent, of moisture. 



Because of the readiness with which moisture passes from 

 plants into the atmosphere, large quantities must be taken 



Fig. 34. — The effect of increasing water supply on the production of dry- 

 matter in various crops. The water is expressed in acre-inches. 



from the soil in order that the plant may maintain its proper 

 turgor. That the crop may be properly supplied with water, 

 optimum moisture conditions should prevail in the soil at 

 all times during the growing season. It must not be inferred 

 that loss through the plant is the only means by which mois- 

 ture leaves the soil, since drainage and evaporation are by 

 no means insignificant factors. 



