The Environment . 39 



Sangre de drago (Jatropha spatulata). 



This plant is a very characteristic xerophyte, and is found beyond 

 the limits of the Chihuahuan desert, westward into Sonora (MacDougal, 

 1908). The upper part of the plant consists of a simple, dark-brown 

 and somewhat fleshy stem, scarcely branched at all and slightly curved. 

 The leaf-producing lateral shoots are very short, and are roughened with 

 small scales; from them arise the bright green narrow leaves in clusters. 

 Reproduction takes place readily by means of seed, and the plant spreads 

 by underground stems which are thick and fleshy, and are, in fact, water- 

 storage organs. Like the lechuguilla it is a colonial form, growing in 

 dense patches, but is less able to occupy the ground to the exclusion of 

 other plants because of the slender aerial parts. Its ability to take up 

 large amounts of water from the superficial soil must, however, be reck- 

 oned with. There is little doubt that this is a dominating type. 



Rastrero (Opuntia megalarthra). 



This is a spreading, low form of prickly pear. Though sometimes 

 very densely packed, making progress difficult, mechanically it interferes 

 comparatively little with guayule. This is to be explained by the fact 

 that, on account of the edgewise position of the flat, procumbent branches, 

 very little soil surface is actually occupied. One finds, indeed, that young 

 plants of guayule are frequently abundant in irregular rows beneath, or 

 nearly so, the branches of the opuntia. It is not unlikely that the spines 

 of the former aid somewhat in protecting the guayule from jack-rabbits 

 and other predatory animals, and so, in this particular respect, help it 

 along rather than hinder it. While this opuntia is a persistent type, its 

 occupancy of the ground is apparent rather than real. 



A composite shrub (Zexmenia brevifolia), huisache {Acacia farnesi- 

 ana) , gatuno (Acacia greggii) , and asafran (Buddleia marrnbiifolia) are all 

 shrubby, freely branching kinds. The last resembles guayule in color, 

 and the novice may easily mistake the one for the other. The gatuno 

 and huisache are small trees with slender branches, and make but little 

 shade. The nature of the competition between these forms and lechuguilla 

 is more evident than in the case of these and guayule. They are slow- 

 growing and do not reproduce themselves except by seed, and this not 

 rapidly. Nevertheless, excepting the gatuno, they may be found growing 

 very plentifully in some situations and often outnumber the guayule. 

 Thus on north slopes the composite shrub is frequently more numerous 

 than the guayule. 



Peyote (Peyotl) (Lophophora williamsii and L. lewinii). 



These cacti are the mescal-buttons or dry whisky of the Texas In- 

 dians and cow-men, and have been sought after as the source of a little 

 understood alkaloid of marked effects upon the nervous system. The 

 exposed part of the plant is little more than a convex disk a few centi- 

 meters in diameter, of fleshy texture. The stem and root together form 

 a conical, fleshy mass. They are a very modest element in the vegetation, 

 occupying little surface, and may be disregarded from a practical point 

 of view. 



