478 MEMOIRS OF THE NEW YORK BOTANICAL GARDEN 



Wyoming; and the Northern Rockies from the Wind River 

 ^Mountains in central Wyoming northward. To the former may 

 be ascribed also the Uintah, Wasatch, and several other smaller 

 ranges in Utah. As belonging to the floral district of the Northern 

 Rockies are to be counted several more or less isolated mountains 

 in Idaho, Montana, and Wyoming. The Cypress Hills in Sas- 

 katchewan and the Black Hills of South Dakota and Wyoming 

 may also be included therein, though both contain many eastern 

 elements. 



The division between Northern and Southern Rockies is not 

 made wholly because there is a break in the high mountain chain, 

 about where the Union Pacific Railroad crosses Wyoming, but 

 because many plants are restricted to either region and do not 

 cross the gap. The floras of the two regions show many differ- 

 ences, especially is this the case of the more characteristic species 

 of the wooded areas. It is true that many of the trees, as Picea 

 Engelmanni, Pinus scopulorum, P. Murray ana, and P. flexilis, 

 Pseudotsuga mucro?iata, Abies lasiocarpa, Sabina scopulorum, 

 Betiila fontinalis, Alnus tenuifolia, and several species of Crataegus, 

 Salix, and Populus are common to both regions, but others are 

 not. Pinus aristata, P. ediilis and P. nionophylla, Picea Parryana, 

 Sabina monosperma and S. titahensis, Populus Wislizeni and P. Fre- 

 montii, Fraxinus anomala and the oaks of the Quercus Gambelii and 

 Quercus undulata groups are practically restricted to the southern 

 Rockies. Of these only Picea Parryana has been collected in 

 what I consider as belonging to the Northern Rockies, namely 

 in the Teton Mountains of western Wyoming. It is between 

 these mountains and the Bear River Mountains of southern 

 Idaho (an extension of the \A'asatch), not along the continental 

 divide in central Wyoming, that an interchange of species 

 between the two regions takes place. Hence some northern 

 species are found in southern Idaho and northern Utah, but not 

 in southern Wyoming, and a few southern ones in the Tetons. 



The wooded flora of the Sierra Madre shows still more striking 

 differences, but this would lead us outside the present discussion. 



In the Rocky Mountains proper I am inclined to recognize the 

 f()ll(nving zones: (i) Alpine; (2) Sul)alpine; (3) Montane; (4) Sub- 

 montane or Foothills; (5) Upper Sonoran. These correspond 

 practically to Dr. Merriam's life zones: Arctic, Hudsonian, 



