ta UNITED STATES AND MEXICAN BOUNDARY. 
borders upon the valley is broken by deep ravines, and we find here upon the sandy blufis a 
growth of chaparral, made up principally of mezquit and the equally thorny acacias. In the 
dry pebbly water courses, the willow-leaved Chilopsis linearis frequently occurs. Many of the 
already mentioned plants of the table land are found here, besides others, which are peculiar to 
these localities, such as Dithyre wislizenti, Abronia mellifera, Gilia longiflora, Lepidium 
alyssoides, Gaillardia pinnatifida, Раїајохіа Hookeriana and Tetraclea Wrightii, a singular 
genus of Verbenaceae, recently described by Dr. Gray. In the valley of the Rio Grande we 
frequently find a heavy growth of cotton wood and willows. The ‘‘ screw bean,” Strombocarpa 
pubescens, often occupies large tracts, accompanied by a dense undergrowth of Baccharis salicina. 
The low saline places produce an abundance of Obione canescens, while on the higher ground, 
Tessaria borealis is a common plant. 
A number of coarse composite plants are found in the valley, such as T'ezmenia encelioides, 
Coreopsis cardaminefolia and Aster spinosus, the latter often forming dense matted masses of 
considerable extent. 
The rocky crevices of the adjoining mountains furnish some of the most interesting plants of 
this region. We here find Fendleria rupicola, Mortonia crassifolia, Glossopetalon spinescens, 
Agenia parvifolia, Bouvardia hirtella, Tecoma stans, Texmenia brevifolia, &c. 
The higher mountains of the Organ range have a vegetation possessing a somewhat alpine 
character, and bear a scattering growth of pines and oaks, beneath which flourish a number of 
shrubby and herbaceous plants, quite similar to those found upon the more lofty ranges further 
to the west. 
VEGETATION OF THE SIERRA MADRE. 
As we approach the base of the Sierra Madre, passing over the extensive basin-plain 
already described, a gradual increase in the elevation is marked by a disappearance of those 
plants, which were common lower down, and the presence of others wearing a more alpine 
aspect. The surface is less bare than upon the plain below, and is covered with a closely matted 
grass, which gives a singularly rounded outline to the undulating land around the base of the 
mountain. Along the lower rocky swells grows the beautiful Carphochete Bigelovii, with 
Anemone Caroliniana, Streptanthus linearifolius, Pentstemon Torreyi and Fendleri are among 
the characteristic plants of these localities. There are but few shrubby plants, several species 
of Ephedra being among the most conspicuous. The streams are bordered by Fraxinus velutinus 
and Juglans rupestris, (the large variety,) and in moist places an old Californian acquaintance, 
Anemiopsis Californica makes its appearance. 
Upon the mountains oaks and pines are found, mostly Quercus Emoryi and Pinus edulis, 
though in certain localities there is larger timber, consisting of Pinus Chihuahuana and Abies 
Douglasti, The smaller woody growth here includes several species belonging to thé Californian 
mountain flora, such as Cercocarpus parvifolius and Arctostaphylos tomentosus. 
Upon the summit of Ben More, further to the north, Dr. Bigelow discovered many plants 
indicative of an alpine flora, among these were Frasera speciosa, Rubus Neo-mexicanus, Actinella 
Richardsonii, and, perhaps, most remarkable of all, a small fern, Asplenium septentrionale, an 
European species not before detected on this continent. 
The abrupt descent through Guadaloupe pass, upon the western slope of the ridge, presents 
a profusion of evergreen shrubs and flowering plants, including most of those which occur on 
