Ko.i.] GRAY AND HOOKER ON THE ROCKY MOUNTAIN HLORA. 33 



or three species on the Pacific side, the reduced type Flcerlcea on the 

 Atlantic side also ; all wanting to the Rocky Mountain flora. 



OxALiDE^.— A very few species of OxallH, one peculiar to the east 

 and one to the west, one to the east and middle, and the 0. corniculata 

 both east and west. 



Balsamine^. — Two species of Impatiens in the Atlantic States; none 

 farther westward. 



RuTACEiE. — Mainly a tropical and subtropical order and not largely 

 American, it is only to be noted that the Rutece are represented along 

 the southern border by Thamnosma, a Texan species of which reaches the 

 soutlu-rn Rocky Mountains, and another belongs only to the southern 

 border of the Great Basin. Ptelea extends quite across the continent, 

 whether in one or in three species is uncertain ; and two species of Xan- 

 thoxylum are restricted to the Atlantic border. Cneoridium is a little 

 Californian shrub which rather belongs to this order. The American 

 Simarubaceae axe south of our range. 



Oyrille^. — Two strictly Atlantic genera, one tropical American 

 and a West Indian one, compose the group. 



Aquifoliace^ are represented only in the Atlantic flora by a dozen 

 species of Ilex and the peculiar monotypic genus Nemopanthes. 



Celastraceje. — The single Gelastrus is restricted to the Atlantic 

 flora, which has also two species ot Euonymus ; the Pacific coast has 

 one. Pachystima is a genus of two species, one common through the 

 mountains from the Pacific to the Rocky Mountains, the other extremely 

 local in the Alleghanies of Virginia. 



RHAMNAf:EJE. — Excluding the Texano-Arizonian forms and the sub- 

 tropical of Florida, we are concerned only with Bhamnus and Frdngula, 

 one species of which crosses the continent northward, two Atlantic only, 

 and two Pacific; Sageretia and Berchemia, each having one Atlantic 

 coast species ; and the great American genus Ceanothns. The original 

 species and three others are restricted to the Atlantic flora; three are 

 Mexican ; but the rest, twenty or more species, belong to the Rocky 

 Mountains, where there are few, and to the Pacific flora, where they are 

 perhaps the most abundant and characteristic shrubs, forming a large 

 part of the chaparral. 



ViTACE^E. — Ampelopsis belongs to the Atlantic flora, but reaches tlie 

 southern Rocky Mountains. Vitis has eight or nine species in the same 

 flora, and is therefore more developed here than in any other part of the 

 temperate zone. California has one species ; the Roclcy IMountains and 

 their outlying districts none at all. 



Sapindace^. — Most largely tropical, except that there is a Sapindns 

 along the southern frontiers ; are represented only by certain genera. 

 Four species of ^scmZms characterize the Atlantic flora; one, of a dif- 

 ferent type, the Pacific flora ; and there is none between. Five species 

 of Acerave peculiar to the Atlantic, two to the Pacific llora ; one occui-s 

 only in the western Rocky Mountains; one is common to the latter and 

 3 GH 



