No. l.l GRAY AND BOOKER ON THE ROCKY MOUNTAIN FLORA. 21 



Spiraea discolor, which in its various forms flourishes under exceed- 

 ingly different altitudes. 

 Spircea Millefolium, which is quite peculiar to theGreal Basin. 

 8pirasa ccespitosa should be added, although it spreads in mats over 



the lace et' rocks, concealing its trunk, instead of rising into the air. 



Coleogyne ramosissima, a highly peculiar genus of a single species, 

 found only on the southern border of the Great Basin. 



"Prunus Andersonii, of the Amygdaleous type, restricted to its south- 

 western rim. 



Hardly elsewhere is such an assemblage to be found. Of other shrubs, 

 \othus velutinus and Ribes cereum are the most widespread and abun- 

 dant. One species of Ephedra extends along the mountains almost to 

 the northern border of the Great Basin, and two or three more are 

 among the characteristic shrubs of the region south of it. 



As to herbs, the genera and the groups mentioned above as predomi- 

 nant at a greater elevation (especially (HUa, Pentstcmon, Phacelia, and 

 <ionum) still play a prominent part. Astragali become more numer- 

 ous, as also do white-flowered species of CEnoth-era^and llelianthoideous, 

 Belenioideous, and Seneeionoideous Composite are conspicuous, yet not 

 more so than in other parts of iSTorth America. Few Composite are 

 peculiar To this zone, and few genera are peculiar to the Rocky Mount- 

 ain region as distinguished from the Californian. The more character- 

 istic genera of the whole region may be adverted to in another connec- 

 tion. 



2. The arid or desert interior district, namely, that between the Rocky 

 Mountains and the Sierra Nevada, the central part of which is the 

 at Basin proper, with no exterior drainage, but which also extends 

 north between the Rocky Mountains and the Cascades, and is there 

 drained by the Columbia River, and far south over the district through 

 which flow the waters of Rio Colorado and the Gila, with also an exten- 

 atern outlier between the Wahsatch and the Colorado Rocky 

 Mountains, and, as well, north of the Uintas, drained bytheGreen River, 

 the main and farthest source of the Colorado, where an arid woodless 

 trad, with all the features of the Great Basin, broadly intersects the 

 wooded Rocky Mountain ranges. The mountains which traverse and 

 diversify these deserts are thought to occupy about half the area, and al- 

 though many of them appear to be as bare as the intervening valleys, 

 yel their varied surface and exposure and the condensation of moisture 

 which they compel, even from an unwilling air. nourish a different 

 etaiion. consisting of a larger number of species. This having already 



been noted, only the botany ot the valleys and plains IS under present 



consideration. 



The region, in a genera] botanical view, is one of undershrubbiness ,- and 



the prevalent growth is composed of Artemisia*) Chenopods, and li.u r - 



funall-flowered Composite. It cannot be better described than 



