DEFINITIONS 25 
classification there is an unavoidable overlapping. 
However, no one factor so fully represents varying 
degrees of aridity as the annual precipitation, and 
there is a great need for concise definitions of the 
terms used in describing the parts of the country 
Fic. 10. Sagebrush growing in infertile sandy soil under an annual rain- 
fall of less than 10 inches. Utah. 
that come under dry-farming discussions. In this vol- 
‘ume, the terms ‘‘arid,’”’ ‘ semiarid,” ‘‘ sub-humid ” 
and ‘‘ humid” are used as above defined. 
Precipitation over the dry-farm territory 
The map on page 23, based upon the work of 
Professor A. J. Henry of the United States Weather 
Bureau, shows graphically the normal annual pre- 
cipitation in the United States of America. Exami- 
