364 Rydberg: Phytogeographical notes 



about 60 per cent, are also found in the Montane Zone or pine 

 belt. This leaves only about 10 per cent., which are restricted to 

 the Subalpine Zone. The percentage of characteristic subalpine 

 species is, however, larger, probably 25 per cent, or 30 per cent, of 

 the number, for the 30 per cent, growing above the timberline is 

 divided into two categories, alpine plants descending below the 

 timberline, and subalpine species ascending above the same. So 

 are also some of the plants which are common to the Subalpine 

 and Montane Zones, essentially subalpine, though they descend 

 into the upper part of the Montane Zone. A small proportion is 

 even common to the three zones, and a few, as for instance Poa 

 crocata, range from the plains to the alpine regions. 



Of the eight hundred species, over 20 per cent, are transconti- 

 nental plants, and of these the larger part, about 15 per cent, of 

 the whole number, extend as far south as Colorado and scarcely 

 2 per cent, are confined to the Canadian Rockies. About one 

 hundred species are common to the old world. Besides the trans- 

 continental element nearly 20 per cent, more are common to some 

 part of the Rocky Mountain region and some part of the Pacific 

 mountains. Of these about 5 per cent, are equally distributed 

 throughout both provinces and 6 per cent, limited to the northern 

 part of both. The remainder is about equally divided between 

 Rocky Mountain plants which have invaded the Cascades and 

 Pacific plants found in the Northern Rockies. 



The strictly endemic species constitute nearly 60 per cent., and 

 if those which have invaded the Pacific mountains are added the 

 endemic element comprises about 70 per cent, of the flora. Of the 

 60 per cent, of strictly endemic plants fully one half are restricted 

 to the Southern Rockies, fully one fourth common to both, and 

 less than one fourth restricted to the Northern. 



Of the trees and shrubs found in the Subalpine Zone, eighteen 

 are transcontinental, eighteen are common to the Pacific moun- 

 tains or emigrants from them, nine are immigrants into the Cana- 

 dian Rockies from arctic regions, and eighteen are endemics, five 

 of which have invaded the Cascades. Of the endemics, eight are 

 common to both the northern and the southern Rockies, and five 

 are limited to each region; none of them are strictly local. 

 New York Botanical Garden 



