38 Guayule. 



growth of guayule than that from which lechuguilla is absent. For 

 although it would seem that germination and early growth are favored 

 by the protection offered by the lechuguilla, as a matter of observation 

 one finds but few young plants of guayule in such situations. One reason 

 for this is, probably, that the guayule seeds (achenes) find difficulty in 

 reaching the soil, because the leaves of the lechuguilla catch them and 

 hold them in their axils till they die, thus materially reducing the num- 

 bers which reach the ground. Aside from the consideration that the 

 lechuguilla takes up from the soil its quantum of water, its effect upon 

 guayule is unfavorable, therefore, because of its superior powers of pro- 

 gressively and steadily occupying the ground, and because of the loss 

 of guayule seed by being caught in its leaves. Lechuguilla appears to 

 be an increasingly dominating type in every situation where it gains 

 a foothold. It is common to every part of the foot-slope and in the 

 hills throughout the range of guayule. The great quantity of it to be 

 found produces in many parts of the mesa central the dominating yellow- 

 green coloring often seen there. When it and the guayule are associated, 

 the green is dotted by the gray of the latter, although other plants also 

 may contribute this subdued note in the coloring. 



GOBERNADORA (COVILLEA TRIDENTATA) AND OCOTILLO (FOUQUIERIA SPLENDENS). 



These may be considered together. Their forms are similar because 

 of the habit of their slender branches, which arise from near the base 

 and reach obliquely upward, producing the effect of an inverted cone. 

 They are both taller than guayule, but the shade cast by them is small 

 in amount, and less is cast by the ocotillo than by the gobernadora. The 

 only places where the ocotillo grows thickly are in certain situations on 

 south slopes, and here it often forms a dense thicket. When thickly grow- 

 ing it would interfere with the rapid harvesting of guayule because of the 

 thorny branches, but, excepting for the draft it makes on the soil for 

 water, the effect upon guayule is negligible. This applies about equally 

 to gobernadora, which in North Zacatecas, however, reproduces itself quite 

 rapidly by seed, and so may readily come to occupy too much ground. 



PALMA SAMANDOCA (SAMUELLA CARNEROSA) AND SOTOL (DASYLIRION CEDROSANUM). 



These are similar in form. Each plant has a single stem supporting a 

 large rosette of leaves. The sotol, however, rarely rises sufficiently above 

 the surface of the soil to free the surface from the lower dead leaves, 

 which cover about 10 square feet of area. Both plants are valuable eco- 

 nomically, the palma samandoca affording a fiber of less value than the 

 lechuguilla, but of which a good deal is prepared, while the other is the 

 basis for the manufacture of the whisky -like liquor, mescal sotol, or simply 

 sotol. Neither of these occurs in sufficient numbers to figure in compe- 

 tition with the guayule within its proper habitat. Indeed, for reasons not 

 yet understood, when sotol grows densely, forming a chaparral, guayule is 

 entirely absent. One reason, if not the only important one, is that the 

 sotol appears not to be confined to limestone areas, but is not excluded 

 from them. 



