INTRODUCTION. 



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incisions made at certain seasons of the year, and e^speclally by the proximity of fire ; facts which 

 may he turned to account if the gum yhould ever be collected as an article of commerce. 

 Growing with the mezquite, though preferring a moister soil, is the Stromhocarpa puhcscens^ 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 mez(]^uite. The fruit is also u. ed as food for animals, but is less 

 valuable than that of the mezquite. 



The principal undergrowth consists of Tcssaria horealis, a shrubby composita, which grows 

 upon light dry soil in thick masses. Its straight branches are 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, wdiich 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. Torrcy's Appendix to Emory's Report. 



A kind of soft cane graps (Arundo niragmites) grows along the river's margin, and is the 

 principal reliance for fodder in this region. Two other kinds of grasses arc 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 reaohv^s 

 the valley of the Colorado; these furnish some of the most interesting plants in the district. 

 Here we again encounter the silvery chajiparal tree, before noticed, (Dalea spinesceiis;) also, 

 another of the same natural family, Olneija Tesota^ {^^^Jj PI- Thurb.) This is a 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 Eeport as the *^ green-barked acacia" of the 

 valley of the Gila. This is Cercidium Jloridanum ; 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 fiimily are represented by a 

 slender, cylindrical, much branched, and horribly spinose Opuntta, (0. 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, hut 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 a country exposed to an 

 unmterrupted drought of seven months duration in each year. Though the verdure has if ^^ 

 vivid freshness of spring, but is even inclined to a leaden hue, yet the relief to the eye v;?\ ' 

 readily appreciated when contrasted with those complete deserts, whose universal barrenn 

 seems increased rather than relieved by the repulsive spine-clad cacti or bristling yuccas. 



Another peculiarity is the general prevalence of a balsamic odor. This is especially true uf 



