118 



OUTLINE OF PLANT GEOGRAPHY 



species of buffalo-berry (Shepherdia) , raspberries, currants, sumac, 

 huckleberries, plums, and others. 



Crossing the divide to the west side of the range, one finds within 

 less than twenty miles a remarkable difference in the forest 

 vegetation, due to a marked change in climate. The west side 



Fig. 28. — Forest, Glacier National Park. At right, center, cotton-wood (Populus 



trichocarpa) . 



of the range evidently intercepts a large share of the moisture 

 brought by the west winds from the Pacific, and the rainfall is 

 consequently very much greater than on the eastern side of the 

 mountains. Moreover the winter cold is much tempered by the 

 westerly winds. 



The forest about Lake McDonald at the western base of the 



