250 Plant Life and Evolution 



vegetation of the south polar zone is so scant as to 

 practically amount to nothing. 



The Sub-polar Zone. In the sub-polar zone 

 generally, much the same conditions, except tem- 

 perature, prevail as were found during the pre- 

 glacial epoch, and there is the same uniformity 

 of vegetation, which, however, is much scantier, 

 as might be expected from the more rigorous cli- 

 matic conditions which now prevail. Throughout 

 this area, from Northern Scotland and Scandinavia, 

 to Eastern Canada, the same types give character to 

 the vegetation. Poplars, willows, firs, and birches 

 are the predominant trees, and in the mead- 

 ows and bogs many beautiful flowering herbaceous 

 plants give a charm to the brief summers of these 

 high northern regions. Of course there are many 

 plants in Canada and Alaska which do not occur in 

 the Old World, but these are mostly emigrants from 

 the South and may be said not properly to belong 

 to the sub-polar zone. 



The North Temperate Zone. Proceeding south- 

 ward from this uniform northern zone of vegeta- 

 tion, the increasing warmth causes a corresponding 

 greater diversity in the vegetation, this diversity 

 becoming more and more marked as the warmer 

 tropical zones are approached. As the temperate 

 zones of the Old and New World are now com- 

 pletely isolated, and have been so since the close of 

 the Glacial epoch, a very much greater difference 

 between the floras of the Old and New World is 



