HOW FORESTS FEED CLOUDS 



217 



portions of the United States, the moister must be the 

 air in the central states and the more precipitation 

 must fall there. 



The central interior region of the United States is 

 the battleground of two titanic forces, of which one is 

 harmful and the other beneficial. The beneficial force 

 takes its origin in the Gulf of Mexico and the adjoining 



PRECIPITATION SHOWN BY 



LINES AND riGURW 

 WIND StlOWN 6Y ARROWS 



WIND DIRECTION AND MEAN PRECIPITATION TOR THE MONTH OFJULY 



ocean, the harmful in the interior of the contintent and 

 the Rocky Mountain region. The central states and 

 the prairie region are geographically at the point where 

 the battle between the two forces is fiercest and the 

 victory is now on the one side and now on the other, 

 being dependent on the cold and humid and the warm 

 and dry climatic cycles as well as upon the seasons of the 

 year. When the humid southerly winds extend their 



