The Environment. 

 A few of the more obvious of these are: 



37 



The above enumeration indicates that at the present time the guay- 

 ule in this habitat is far and away the most important plant numerically, 

 and is therefore dominant in the usual sense. Whether it will continue 

 so whether its dominance is waxing or waning may be indicated by 

 the relative numbers of guayule plants of different ages and by the inter- 

 action of the various elements in the vegetation. 



We may therefore consider briefly each of the numerically most im- 

 portant species. 



LECHUGUILLA (AGAVE LECHEGUILLA). 



While the actual number of plants of this species found in quadrats 

 5 and 6 is much larger than that of any other save guayule, it is very 

 small compared with the number which is found on much guayule land 

 (e.g., plate 5, fig. B). 



In common with the Agaveae, the plant propagates itself chiefly by 

 means of stolons which lie a few centimeters below the surface. In this 

 way it spreads from an original plant radially, taking up the ground as 

 it goes, from which nothing but death dislodges it. In the course of a 

 few years it attains maturity, when a tall flower-stalk is developed; then 

 the whole individual, consisting of a single cluster of leaves attached 

 to a short (10 to 15 cm.) and thick (6 to 7 cm.) stem, dies. Where the 

 lechuguilla has occupied the ground for some time, it frequently forms 

 a dense growth, from which other plants, save a few annuals or emaciated 

 perennials, are excluded. Its manner of spreading, by which it repro- 

 duces itself vegetatively , enables the plant to occupy areas in which the 

 soil is confined to the crevices of the rocks, and in this manner it may 

 occupy ground which is unfit even for those desert plants with which 

 it is usually associated. From it is extracted the fiber "ixtle tula," or 

 "ixtle de lechuguilla," which is of considerable commercial importance, 

 and thus the plant is of some value not, however, sufficient to justify 

 it as a competitor of the guayule. The method of vegetative reproduc- 

 tion above noted is also characteristic of the guayule (Lloyd, igoSc), 

 especially when growing where the country rocks come to the surface, 

 but is in this plant of relatively much less importance. 



The mutual behavior of these two plants under strong competition 

 is not very easy to describe precisely. It seems clear that, with the excep- 

 tion of a few plants which succeed in gaining a foothold by germinating 

 in the shade between plants of lechuguilla, sometimes being favored 

 by the protection from drying out and from cropping by animals thus 

 afforded, ground occupied by lechuguilla is much less favorable for the 



