288 Part III. Chapter 3. 
difficult to arrange the species zonally, because the flora of any mountain 
locality is greatly influenced by a warm and sunny exposure, or the opposite, 
The endemic mountain species of the Basin are described in Part IV, Chapter Il, 3. 
The Great Basin has supplied many species to the Rocky Mountain region 
and beyond to the east, while a similar element is found in Oregon and 
Washington and western Texas. These elements have been previously de- 
scribed and a discussion of them will be omitted at this place. Looking at 
the Basin flora, as a whole, it appears to.be to a considerable extent a distinct 
one. Though the position of the territory would rather indicate as probable 
an intermingling of the surrounding floras, of the Californian with that of the 
Rocky Mountains, and of the extreme northern descending along the mountain 
ranges, with that of the deserts of Arizona, spreading northward in the valleys, 
yet it has a marked character of its own. This consists partly in the absence 
of many of the peculiarities of the surrounding floras.. A very large portion 
of the Pacific species, not only arborescent, but shrubby and herbaceous, stop 
abruptly upon the eastern slope of the Sierras and do not reappear eastward. 
A like demarcation is shown on the eastern side at the base of the Wahsatch 
Mountains by the intermediate accession of new orders and species, characteristic 
of the eastern flora. Again many of the forms prevalent farther south are 
wanting, or appear only on the borders of Nevada and Utah, as most of the 
Cactaceae and of the Daleas and other large leguminous genera and suborders, 
characteristic rutaceous, zygophyllaceous species, the Cucurbitaceae, Loran- 
thaceae, a large portion of the Solanaceae, Euphorbiaceae and Nyetaginacea® 
The mingling with northern species is necessarily more intimate. The general 
preponderance of senecioid composites (Artemisia tridentata, the prevailing 
presentative) and the marked number of chenopodiaceous genera and spec!” 
many of which do not extend beyond the limits of the Basin, make the flora 
a singular one and warrant designating the district as one of Artemisias and 
chenopods. The abundance of species of Aszragalus, Eriogonum, Oenothera, 
Pentstemon and Phacelia is also more or less distinctive. The southwesief 
portion of the Sonora-Nevadan Desert includes the limits of two Very distinet 
districts, comprising the territories of the Mohave Desert and of the Colorado 
Desert. The Mohave Desert district, may be looked upon as belonging he 
the Great Basin Region, while the Colorado Desert has greater affinities with 
the desert flora of Mexico (see the map: Sonoran Desert region). ! 
The Colorado and Mohave Deserts.. These have many plants which ar 
a ge but each possesses also a distinctive flora. It appear En 
nn ee; » the desert genera fall into three nearly iz | 
those wich a % eg end re ! 
a northeastern E Er E ie en er er ee be = Utah 
and the Great Basin; ai BER ee Ye Mn Be whose 
a ‚and a southeastern section to include the gen“ 
ge are into northern Mexico. A number of spec” 
diverse ranges and the genera to which they belong are indicated. 
