THE WATER-COST OF DRY MATTER 



133 



duced that the transpiration ratio would always be the 

 same. If the increase in dry matter were thus always pro- 

 portional to the quantity of water transpired, it would 

 simplify greatly many important problems of agriculture. 

 Such a definite relationship, however, was not found, and 

 it is now well known that every agricultural practice 

 influences not only the assimilation of carbon but, also, 

 transpiration, though not always to the same degree or 

 in the same direction. Transpiration and the production 

 of dry matter are only in part interdependent; to a much 

 larger degree they are independent of each other. This 

 is a fundamental thesis of irrigation agriculture. 



Many investigators have determined the number of 

 pounds of water required for the production of one pound 

 of dry matter of various crops on a variety of soils and in 

 several countries of the world. Some of these determina- 

 tions are collected in the following table: 



It may be noted that the transpiration ratios are lower 

 in England and Germany, under humid conditions, than 

 in Utah and India, under arid conditions. This is a general 



