SUMMARY. 91 
the least efficient in producing dry matter with a given amount of 
water. The small-grain crops have a water requirement intermedi- 
ate between the legumes and corn. Measurable differences in the 
water requirement also exist between different varieties of the same 
crop, and this suggests the possibility of developing through selection 
strains which are still more efficient in the use of water. 
Leather found that the water requirement of a crop grown under 
field conditions was, as a rule, lower than the water requirement of 
the same crop determined from pot experiments. The writers' meas- 
urements of the water requirement of wheat under field conditions 
gave a higher value than the corresponding pot determinations. If, 
however, the calculations were based upon the amount of stored 
moisture removed by the crop without reference to the rainfall 
received during the growing season, the field results were in close 
agreement with the pot experiments. 
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