ARID AGRICULTURE. 23 



freezing which totally destroys the same plants 

 at the end of the season. Technically the grow- 

 ing season runs through almost the entire year, 

 even where the winter is severe. Winter grains 

 and the native grasses undoubtedly extend their 

 root systems after the crops are frozen dormant 

 and the tops make considerable growth during 

 warm days, even if the nights are very cold. It 

 is important to plant crops early enough so those 

 subject to frost injury w^ill mature before early 

 frosts come. Spring grains and tender vegeta- 

 bles are in this class. How advantage may be 

 taken of the growing season depends upon the 

 character of crop grown and the particular cli- 

 matic conditions of each region. 



RAINFALL OP The total precipitation is less than fifteen 

 inches per year. The character of the precipita- 

 tion and the time it comes varies greatly. In 

 the region west of the Rocky Mountains the 

 larger part of the moisture falls in the winter 

 months and the summers are dry. East of the 

 Rockies as much as seventy-five per cent, of the 

 total moisture falls in the spring months W 7 hen it 

 is most useful for the germinating seed and the 

 early growth of plants. Where irrigation is de- 

 pended upon it is important to store a part of 

 the flood waters and the run-off from early melt- 

 ing of mountain snows into reservoirs for the 

 supply of late water when the streams are low. 

 The dry farmer, where winter rains prevail, 



