12 Rydberg: Phytogeographical notes 



about 2,000 m. (6,500 ft.), and in the Selkirk Mountains of 

 British Columbia still lower. 



A region which extends twenty degrees in latitude* will 

 naturally not be homogeneous, as far as its vegetation is con- 

 cerned. It also can be divided into two principal parts: the 

 Northern and the Southern Rockies. In Wyoming, about where 

 the Union Pacific Railroad is drawn across, there is a break in the 

 high mountain chain. This break may be regarded as the division 

 line between the Northern and the Southern Rockies. 



The larger part of the Southern Rockies is within the state of 

 Colorado, but they extend south into New Mexico to Santa Fe, 

 and northward into Wyoming, where they are known as the 

 Medicine Bow Mountains. West of the Southern Rockies and 

 separated from them by the Green River basin are the Uintah 

 and Wasatch Mountains. The former have practically the same 

 flora as the Southern Rockies, but the western slope and southern 

 end of the Wasatch Range partake of the floral nature of the 

 isolated mountain chains of the Great Basin. The northern end 

 of the Wasatch Mountains, the range enclosed by the horseshoe 

 bend of the Bear River in southern Idaho, is the most northerly 

 extension of the floral district of the Southern Rockies. It is here 

 and across the Bear River in the Teton Mountains, not along the 

 continental divide in Wyoming, that the floras of the Northern 

 and Southern Rockies meet. 



The Northern Rockies form an uninterrupted chain from Yukon 

 Territory to the Wind River Mountains in Wyoming and the 

 flora is practically homogeneous, except the western slope of the 

 northern portion. To the Northern Rockies should also be 

 counted several more or less isolated mountain ranges, as the 

 Saw-tooth Mountains of central Idaho, the Tetons of w^estern 

 Wyoming, the Cypress Hills in Saskatchewan, several ranges in 

 Montana, the Bighorn Mountains in northern Wyoming and 

 the Black Hills and several smaller chains in their neighborhood. 

 None of these except the Big Horns and the Tetons can be taken in 

 account when the subalpine flora is considered. The Selkirk 

 Mountains between the bends of the Upper Columbia River, 



* My discussion in this paper refers only to the region between 35° and 55° 

 latitude. 



