xliv BOTANY. 



Atlantic species increases to one-fourth and that of the Pacific diminishes to 



three-fifths. 



Looking at the Basin flora as a whole it appears to a considerable 

 degree a distinct one. Though the position of the territory would rather 

 indicate as probable an intermingling of the surrounding floras, of the Cali- 

 fomian 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— as indeed is largely the case— 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 Pacific 

 species, not only arborescent but shrubby and herbaceous, stop abruptly upon 

 the eastern slope of the Sierras and do not reappear eastward. For this reason 

 the Cahfornia district should be considered as limited on the east by that 

 range, the whole southeastern portion of the State and a smaller section in the 

 northeastern part belonging geographically and botanically to the Colorado 

 Desert and to the Basin respectively. A hke line of demarcation is shown 

 on the eastern side at the base of the Wahsatch by the immediate 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 Cactacea, and of the Daleas and other 

 large leguminous genera and even suborders, characteristic Rutaceous and 

 Zygophyllaceous species, the Cucurhitacece and Loranthaceoe, Salvia, and the 

 larger portion of the Solanaceoe, Euphorhiaceoe. and JSlyctaginaceoe. The 

 mingling with northern species is necessarily more intimate, yet with a more 

 exact knowledge of the habitats of " Oregon" species a well marked limit 

 of the Basin flora could probably also be drawn in that direction. But aside 

 from thesedeficiencies, the general preponderence of senecioid composites, 

 of which the Artemisia tridentata imay be considered the prevailing represen- 

 tative, and the so marked number of chenopodiaceous genera and species, 

 many of which do not extend greatly 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 Astragalus, Eriogonum and 

 the allied genera, CEnothera, Pentstem.on, and Phacelia, is also in a more or 

 less degree distinctive. 



The following table shows the distribution of the genera and species 

 arranged by orders ; 



