A Graphic Suninmry of American Agnculture. 



13 



cf^ fi^Ti"^ "'"P '^ much reducod and seneralized from a map prepared bv the L'nitod 

 *i, i**, ^^^'i^^'^' ^ui'^'iu ind publii^bod In the Frost and the Growing season section of 

 A •/! T ?® °^ American Agriculture. The higher altitude of the Rocky Mountain and 

 Arid intermountain Regions (see Fig. 3), and the drier air (see Fig. 4), which permits 

 rapia loss of heat at night, are two important causes of the short ffost-free season, 

 uver much of these regions the frost-free season is shorter than in northern Maine or 

 Minnesota. The powerful influence of the Pacific and the lesser Influence of the Atlantic 

 in lengthening the growing season along their shores should also be noted. 



