248 Part III. Chapter 3. 
Pacific coast plants. It lacks almost entirely elements derived from the Gre: 
Basin region, as well, as many of the peculiar genera of the eastern, or A 
lantic flora. There are, however, many plants restricted to this region which 
in all probability have been differentiated since the close of the glacial perioc 
he mountain systems south of the Bighorn valley, which we have cho 
as a line of separation, may be denominated the southern Rocky mout 
tain region. Its flora likewise possesses negative characters, but it is clearl 
distinct from the northern region by the injection of floral elements deri 
The northwestern element in this flora 
prominent having been in the process of diffusion from the beginning to A 
end of the last glacial recession, because to have entered the southern Roc 
Mountains required a longer time than that subsequent to the final melting 
the glaciers and the drying up of the lakes. 
from Mexico and the Great Basin. 
Acer glabrum Torrey. 
Artemisia dracunculoides Pursh. 
Berberis repens Lindl. 
Celtis occidentalis L. var. reticulata 
Clematis ligusticifolia Nutt.  [Torr. 
Crataegus rivularis Nutt. 
Gaultheria myrsinites Hook. 
Juniperus scopulorum Sarg. 
A number of other trees and shrubs may have entered the southern all 
northern Rocky Mountains of the United States and Canada by the nortb 
western route after the Glacial period, but more likely, they represent a = 
flora of a period, when as species, they were more widespread during a mof 
humid period before subjected to the arid climate which exists in the regio 
at the present day. To be included in this category in all probability 2 
Abies subalpina Engelm. (— A. lasio- 
carpa Nutt.). 
Betula occidentalis Hook. 
Picea Engelmanni Engelm. 
Pinus Murrayana Balfour (= P. con- 
torta var. Murrayana Engelm.) 
» _ponderosa Dougl. 
The migrants which came down the Rocky Mountain system long SuM 
sequent to the great ice age out of the north and east from the eastern P 
of the continent and settled in the southern Rocky Mountain region are: 
Alnus incana Willd. to Colorado. 
Ampelopsis (Parthenocissus) quinque- 
folia Michx. to New Mexico. 
Cornus canadensis L. to Colorado. 
>». _stolonifera Michx. to Colorado. 
Lonicera ciliosa Poir. 
Ribes aureum Pursh. 
»  cereum Dougl. 
Salix chlorophylla Anders. 
Sambucus glauca Nutt. 
N 
Pseudotsuga Douglasii Carr. (=P. 
folia Britt. — P. mucronata Sud 
Sambucus melanocarpa Gray. 
Tetradymia glabrata Gray. 
Crataegus tomentosaL. to New Mexic0 
Elaeagnus argentea Pursh. to Utah. 
Fraxinus pubescens Lam. rare. 
» © viridis Michx. f. to Arizona. 
Juniperus communis L. to New Men 
