264 DRY-FARMING 
While it is undoubtedly true that dry-farm crops 
are naturally drier than those of humid countries, 
yet it must also be kept in mind that the driest dry- 
farm crops are always obtained where the summers 
are hot and rainless. In sections where the precipi- 
tation comes chiefly in the spring and summer the 
difference would not be so great. Therefore, the 
crops raised on the Great Plains would not be so dry 
as those raised in California or in the Great Basin. 
Yet, wherever the annual rainfall is so small as to 
establish dry-farm conditions, whether it comes in 
the winter or summer, the cured crops are drier than 
those produced under conditions of a much higher 
rainfall, and dry farmers should insist that, so far as 
possible in the future, sales be based on dry matter. 
The nutritive substances in crops 
The dry matter of all plants and plant parts con- 
sists of three very distinct classes of substances: 
First, ash or the mineral constituents. Ash is used 
by the body in building bones and in supplying the 
blood with compounds essential to the’ various life 
processes. Second, protein or the substances con- 
taining the element nitrogen. Protein is used by 
the body in making blood, muscle, tendons, hair, and 
nails, and under certain conditions it is burned within 
the body for the production of heat. Protein is 
perhaps the most important food constituent. Third, 
