sunny parterres beckon to the spying trees, prom- 

 ising centuries of occupation if they can stand 

 the climate. 



The rising heat rolling in waves from the south, 

 nearer and nearer, urges on the lagging columns, 

 adding the necessity of avoiding death to the 

 attraction of better homes. 



But the universal return of plants from the south, 

 was prosecuted under vastly different, more de- 

 structive conditions than those of the northern 

 flight. The plants on the return trip were attracted 

 northward along the cool plains, and also, some of 

 them upward on the mountainsides, for it is the 

 same thing in effect, to ascend a mountain for 

 cooler weather as to journey northward. 



Now the first elevations beside a valley are 

 usually low ones, foot-hills, outlying ridges or 

 higher spurs. The plants that ascended these 

 elevations, as the heat came on and proved too 

 severe for their constitutions, were shriveled and 

 burned then and there the last battle ground and 

 altar-places where were immolated the greater 

 part of the vegetable creation of the period. 



THE LONE SURVIVORS. 



Here and there straggling members of a family 

 reaching a locality on the plain or part way up a 

 mountain when the present equilibrium of seasons 

 was established, found themselves suited to the 

 environment and it is the descendants of those 

 plants that are the inhabitants of our plains and 

 mountains to-day. 



These terminals of broken lines of development, 



(9) 



