INTRODUCTION. 28 
incisions made at certain seasons of the year, and especially by the proximity of fire ; facts which 
may be turned to account if the gum should ever be collected as an article of commerce. 
Growing with the mezquite, though preferring a moister soil, is the Strombocarpa pubescens, or 
** screw bean,” as it is called, on account of the twisted form of its pods. It is usually of small 
growth, and is rarer than the mezquite. The fruit is also used as food for animals, but is less 
valuable than that of the mezquite. 
The principal undergrowth consists of Tessaria borealis, a shrubby composita, which grows 
upon light dry soil in thick masses. Its straight branches аге from four to eight feet high ; the 
younger portions of which, as well as the leaves, are covered with a silvery pubescence. In low 
saline places we find several chenopodiaceous plants; Salicornia, among others, which here 
becomes a stout shrub of two or three feet in height. These localities also furnish the singular 
Dicoris, a notice of which appears in Dr. Torrey’s. Appendix to Emory’s Report. 
A kind of soft cane grass (Arundo Phragmites) grows along the river’s margin, and is the 
principal reliance for fodder in this region. Two other kinds of grasses are met with in similar 
situations, the seeds of which are collected for food by the Indians living near the river. One 
of these is a Panicum, the seeds resembling millet. The other has digitate spikes, resembling 
Eleusine. "The flour made from the seeds of these wild grasses is husky, but quite palatable ; 
and it may be remarked, that species of the genera from which it is derived are in common . 
cultivation in the eastern hemisphere. 
Many ravines occur on the eastern edge of the desert, by means of which its drainage reaches 
the valley of the Colorado; these furnish some of the most interesting plants in the district, 
Here we again encounter the silvery chapparal tree, before noticed, (Dalea spinescens;) also, 
another of the same natural family, Olneya Tesota, (Gray, Pl. Thurb.) This is а good sized 
tree, having much the habit of the common locust. Its fruit consists of short irregular pods, 
which contain two large orbicular seeds. The flowers were not seen. We also find here the 
tree frequently referred to in Major Emory's Report as the ‘‘ green-barked acacia" of the 
valley of the Gila. This is Cercidium floridanum ; and in these localities it is quite a large 
tree, resembling the weeping willow in habit. Its long drooping branches bear an abundance 
of pods. 
Fouquieria grows upon all the gravelly hills, and the cactus family are represented by a 
slender, cylindrical, much branched, and horribly spinose Opuntia, (O. ramosissima, Engel. n. sp.) 
Much yet remains to be learned respecting the vegetation of this singular region, especially 
that of the eastern base of the mountain range. Only enough is known at present to prompt 
the desire of a thorough botanical exploration of its floral riches. 
On taking leave of this branch of our subject, we briefly notice a few general facts connected 
with the vegetation of the country under consideration. One of the most striking botanical 
characteristics of this region, and one which attracts the attention of the most casual observer, 
is the great preponderance of evergreen shrubs. This is not only true of the seacoast and 
desert, but also of the higher mountain ranges. "This fact has an important bearing upon the 
aspect of the scenery, which would otherwise be desolate indeed in а country exposed to an 
uninterrupted drought of seven months duration in each year. Though the verdure has not the 
vivid freshness of spring, but is even inclined to a leaden hue, yet the relief to the eye will be 
readily appreciated when contrasted with those complete deserts, whose universal barrenness 
seems increased rather than relieved by the repulsive spine-clad cacti or bristling yuccas. "os 
Another peculiarity is the general prevalence of a balsamic odor. This is especially true of 
