ON TIMBER TREES 



from their sun-loving habit. But in the main the 

 tribes that escaped destruction were those that 

 developed a hardiness that enabled them to with- 

 stand extremes of temperature not far beyond 

 the limits of the ice sheet. Others made their way 

 northward again so soon as the ice sheet receded. 



And as the climate of ensuing ages, after the 

 successive periods of intense refrigeration, every- 

 where retained, throughout the central and eastern 

 portions of America, curious reminiscences of both 

 the tropical and the arctic, the plants that finally 

 repopulated the devastated territories were those 

 that had learned, through the strange vicissitudes 

 of their ancestors, to thrive where the thermometer 

 in summer might rise to the one hundred degree 

 mark, and where in winter the mercury might 

 freeze. 



Such arc the conditions under which pines and 

 oaks and willows and beeches and black walnuts 

 and allied trees exist to-day in the regions of 

 northern America where they flourish. 



They can withstand the glare of a tropical sun 

 in summer because their ancestors reveled in a 

 tropical climate. And they can withstand equally 

 the arctic cold of winter because their ancestors of 

 other ages were forced to subsist under arctic 

 conditions. 



The versatile tree that, thanks to the racial 



[189] 



