LUMBER TREES 121 



scant reminiscence of that of the period preced- 

 ing the ice ages. Only a few species, relatively 

 speaking, were able to make their migration 

 rapidly enough to escape destruction. These 

 included a certain number, like the sequoia and 

 the tulip tree, that were able to reach coigns of 

 vantage that permitted them to exist without 

 changing essentially from their sun-loving habit. 

 But in the main the tribes that escaped destruc- 

 tion were those that were more plastic and 

 developed a hardiness that enabled them to 

 withstand extremes of temperature not far 

 beyond the limits of the ice sheet. Others 

 made their way northward again when 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 east- 

 ern 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 are the conditions under which pines and 

 oaks and willows and beeches and black walnuts 



