I 



VEGETATION OF THE HIGH SIERRA NEVADA. 29 



Phleum alpinum Also circumpolar. 



Phlox douglasii. 



Pinna albicaulis Not south of Montana in the Rocky Mountains. 



Pinus monticola Not south of Montana in the Kooky Mountains. 



Pinus murrayana. 



Polygonum histortoklcs Also circumpolar. 



Pulsatilla ocoidentalis In the Rocky Mountains north of the United 



States boundary only. 

 ltibes cereum. 

 Kibes oxyacanthoidcs saxosum. 



llibes visvosissimum , Also in Utah, but not in Colorado nor southward. 



Rumex geyeri. 



Saxifraga nivalis Also circumpolar. 



Saxifraga punctata Also in Alaska. 



Sedum roseum Also circumpolar. 



Spraguca umbellata Only north of Colorado in the Rocky Mountains. 



Genus confined to western North America. 



Tellima ienella Genus conlined to western ]S'orth America. 



Trifolium longipes. 



Trisetum spicatitm Also circumpolar. 



Valeriana sylratica. 



From this list it appears that nearly one-halt* of these plants are com- 

 mon to the three regions, a fact which emphasizes the community of 

 origin of all our boreal vegetation. About one-third of the whole num- 

 ber are confined to the Sierra Nevada. This is a large percentage for 

 the endemic constituent of any region which climatically so closely re- 

 sembles other portions of the same continental area. Tn this instance 

 the broad geographical isolation of the Sierra Nevada, and the great 

 antiquity of this isolation, may explain the phenomenon. 



The unexpected results of the tabulation are exhibited in the com- 

 parative numerical size of groups (6) and (c). These lists indicate that 

 the flora of -the high Sierra Nevada of California has an affinity quite 

 as close \vith that of the Rocky Mountains of Colorado as with that of 

 the Cascade Mountains of Oregon and Washington. In suggesting a 

 reason for this remarkable and, at first thought, puzzling fact, we 

 shall first group the species of the whole list according to the theoretical 

 course of their original migration. 



In group (d) there are several plants (Pulsatilla ocoidentalis, Pinus albi- 

 caulis, etc.) which, while found in all three regions, are confined in the 

 Kocky Mountains to the district north of Wyoming and Colorado. The 

 floral intercommunication of the northern Cascades with the northern 

 llockies must have been very free in later glacial times, and the plants 

 in group (6), together with the few last indicated in group (d), form a 

 group of which the original center of migration, it is very probable, 

 was in the more western of the two great mountain systems. The 

 plants of group (d), except those just expunged, constitute a group 

 which was in process of diffusion from the beginning to the end of the 

 last glacial recession, and whose distribution therefore became very gen- 

 eral in both meridional and transcontinental directions. The plants 

 mentioned in group (c) appear to have developed during the period of 



