214 



WOOD AX II foi:kst. 



TJOllrEUATUUU, 



Tlie fact that some tiees, as paper Inrcli 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 tlic average temperature, but the extremes wliich largely deter- 



Fitr. 57. Typical Mixed Foi-esl,— Red Spruce, Heiiilocl;, White A sh. 



Yellow Birch, Balsam Pir, and Red iSIaple. Kaquette LaUe, New 



York, f '. .S'. Forest .SVjt/cc. 



mine the habitat of trees of diilercnt 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 (■arth too cold for trees to live. Fiff. (10. 



