496 MEMOIRS OF THE NEW YORK BOTANICAL GARDEN 



scarcely less than the corresponding zones of Europe and North 

 America, 



5. That the Subarctic and Boreal zones of the eastern and 

 middle divisions, although they meet in the north without a barriers, 

 have practically none of the characteristic plant species in common ; 

 the common plants consisting mostly of transcontinental plants, 

 many of which are also found in the Old World or in other life 

 zones. 



6. That the same zones of the middle and western divisions 

 because of the connections in the north between the Cascades and 

 the Rockies have many of the characteristic species in common, 

 especially in the north, and that there is less reason for keeping 

 these two divisions distinct. They could be regarded as one 

 division, if it were not for the absence of spruce and balsam in 

 the southern part of the western division, and the total absence 

 of redwoods, cypresses, sugar pines, and several other western 

 pines in the middle division. 



7. That the Submontane, Upper and Lower Sonoran zones of 

 the Rockies have practically no elements in common with the corre- 

 sponding zones of the Atlantic Coast, being separated from that 

 region by the grass-covered plains. 



8. That the Submontane zones of the middle and western divi- 

 sion, i. e., of the Rockies and the Sierra Nevada, have rather few 

 plants in common, as they arc separated more or less by the 

 Great Basin. 



9. That the Upper and Lower Sonoran zones of these two divi- 

 sions merge, more or less, as there is no real effective barrier. 



10. That the Arctic- Alpine region naturally has no wooded 

 division, that the Subarctic or Subalpine and the Boreal or Mon- 

 tane zones in America have no grasslands of any extent and that 

 the Subboreal, Upper and Lower Austral zones have both wooded 

 regions and grasslands or deserts. 



11. That the Subarctic-Subalpinc zones of both the eastern and 

 middle divisions are characterized by a spruce-balsam forest, 

 though the species are different. That this forest is lacking in 

 the western division, except in tlic Cascades, where the species of 

 the midtlle division ha\e inxaded the zone. In Europe the zone 

 is represented 1)> the dwarf birch belt in the Scandinavian moun- 

 tains, and the region of Pi mis nioiilicola, Ahiiis viridis, and erica- 

 ceous shrubs in the Alps. 



