214 



WOOD AND FOREST. 

 TEMPERATURE. 



The fact that some trees, as paper birch and white spruce, grow 

 only in cold regions, and some, as rubber trees and cypress, only in 

 the tropics, is commonplace ; but a fact not so well known is that it 

 is not the average temperature, but the extremes which largely deter- 



Fig-. 57. Typical Mixed Forest, Red Spruce, Hemlock, White Ash, 



Yellow Birch, Balsam Fir, and Red Maple. Raquette Lake, New 



York. U. S. Forest Service. 



mine the habitat of trees of different kinds. Trees which would not 

 live at all where there is frost, might flourish well in a region where 

 the average temperature was considerably lower. On the other hand, 

 provided the growing season is long enough for the species, there is 

 no place on earth too cold for trees to live. Fig. GO. 



