22 UNITED STATES AND MEXICAN BOUNDARY, 
new Rhumnaceous shrub (Zizyphus Parryi, Torr.) makes its appearance. Upon the hill sides 
here grows a species of Agave, the ** Mezcal'' of this region. The root of this, when prepared 
by a kind of underground roasting, serves as an important article of food for the Indians. Here 
we also find the ‘‘ Spanish Bayonet,” a species of yucca, which presents its spine-armed leaves 
to the traveller. As we proceed, the lower valleys assume a complete desert-like character. The 
“creosote bush” (Larrea Mexicana) makes its first appearance, to be our constant companion 
for the remainder of the journey. Perhaps the most striking plant of these wastes is the 
Fouquieria splendens. This grows in clumps, consisting of from twelve to twenty long wand- 
like branches, which, springing from the main stem close to the ground, rise to the height of 
from ten to fifteen feet; the stems are beset with rows of spines, from the axils of which grow 
small fassicles of leaves. Its bright scarlet flowers only appear at the time when the stalk 
is destitute of leaves, and hence the whole plant has too naked an appearance to exhibit much 
beauty. 
The well-known mezquite, (Algarobia glandulosa,) which we shall notice more particularly 
hereafter, now becomes a common shrub; and near the base of the mountains a species of pal- 
metto is seen growing in the clefts of the rocks. Its appearance in these localities invariably 
indicates the presence of water, though this is frequently found to be too saline for use. 
As we advance upon the desert plain a very distinct character of vegetation presents itself. On 
all the gravelly ridges near the mountains we find the stiff stalks of Fouquieria. In the fur- 
rowed rain-water courses there is usually a growth of shrubbery larger than in other portions 
of the desert. In such situations a small tree of graceful outline occurs—the Dalea spinescens, 
(Gray, Pl. Thurb.) The finely divided branches of this plant are all terminated by sharp 
points, and are covered with a silvery pubescence. It bears a few abortive leaves, and an abund- 
ance of bright blue flowers. Further on in the desert the vegetation is chiefly composed of 
Larrea mexicana and Obione canescens. Near the borders of the lakes and gullies which mark 
the position of ** New river” we find a greater variety among the plants. A very rank growth 
of a species of Amaranthus borders the lakes in wet seasons, and on the upper clay borders of 
‘New river." The annual “Gramma grass” yields, after the rains or the overflows of the 
rivers, a rapid growth of evanescent but highly nutritious fodder. We find in these situations 
a species of Boerhavia and one of Kallstroemia. The mezquite trees near these places attain 
a considerable size, and frequently bear upon their branches a vigorous growth of a peculiar 
misletoe. 
As we descend from the table land of the desert, by the steep bluff which bounds the alluvial 
bottoms of the Colorado river, the vegetation consists almost entirely of dense thickets of mez- 
quite, but it a$sumes a more varied character when we reach the alluvial tracts. On all places 
liable to overflow the cotton-wood and willow abound, the latter forming a thicket along the imme- 
diate margin of the river. The higher grounds near the river seem especially favorable for the 
mezquite, and we find it growing with greater luxuriance than we have seen it elsewhere. In 
some situations it forms thorny and impervious thickets, but it is usually sufficiently scattered 
to permit an easy passage for man or beast. The irregular growth of this tree renders it unfit 
for most of the uses for which timber is needed. As an article of fuel it is scarcely inferior to 
hickory, and the wood is very durable. The fruit of the mezquite is of the greatest value to the 
traveller in these regions. It is a long bean-shaped pod, which is greedily devoured by cattle 
and is found to be highly nutritious. A gum exudes from this tree which closely resembles 
gum arabic in its chemical characters. The production of the gum is evidently increased by 
