ROOT SYSTEMS IN ARID SOILS 89 
condition of the soil permits the entrance of air, which 
helps to purify the soil atmosphere and thereby to 
make the conditions more favorable for root develop- 
ment. Consequently it is to be expected that, in 
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Fic. 25. Corn roots. 
arid regions, roots will ordinarily go to a much greater 
depth than in humid regions. 
It is further to be remembered that roots are in 
constant search of food and water and are likely to 
develop in the directions where there is the greatest 
abundance of these materials. Under systems of 
dry-farming the soil water is stored more or less 
uniformly to considerable depths — ten feet or more 
— and in most cases the percentage of moisture in 
