Vegetation oe the Sotol Country. 
117 
tion of humid climates are absent or unnoticeable in the sotol for- 
mation as also in other arid regions. In the first place, since the 
plants do not stand in close order, they do not influence the growth 
one of another, nor is there that co-operative or mutually dependent 
phase which results in establishing special conditions such as are 
found in a forest with its characteristic soil, light, air, temperature, 
and strata of vegetation. There is scarcely a question of shade 
loving plants here, nor is there evident that phase of dependence 
exhibited by clambering or climbing and twining plants. There 
are few parasites or saprophytes, in short, it is a vegetation of in- 
dependent members. 
But while the various members of the formation are independent 
of each other, there is by no means a uniform aspect of the vegeta- 
tion at ah points. Differences in soil texture, soil moisture, relief, 
etc., are responded to as in other formations and one finds a divi- 
sion of territory as if by common agreement. In some situations, 
the formation involves an association of a majority of all its species, 
in others, a single species is dominant, but in view of their being 
always unoccupied ground a general association may be the ulti- 
mate condition. The more prominent types of association are the 
following : 
Sotol Association: Sotol becomes the dominant species on up- 
land divides and on the even gentle slopes of isolated cones and 
ridges in the more eroded areas. As previously mentioned it is 
the one conspicuous, dominant form which seems worthy of char- 
acterizing the whole formation. There is variation both in the 
closeness or frequence of plants in this association and in the 
height. On the more arid divides, the sotol cover is uniformly 
close but not exceeding two feet in height, while at the head of 
draws where there is more soil and moisture the plants are luxu- 
riant and broad and three to five feet tall . 1 See plates I to IV. 
Lechuguilla Association : This species rivals the sotol in the 
actual extent of territory covered, but in the Langtry district at 
least, it occupies the lower round, topped points and ridges where 
the stony debris is coarser and the conditions more arid than where 
sotol prevails. Mr. Vernon Baily has estimated that the lechu- 
guilla association covers twenty thousand square miles in Texas. 
The plants of lechuguilla stand more thickly upon the ground than 
in the case of sotol, but the pike formed leaves are not so conspicu- 
1 Mr. James H. Gaut of the United States Biological Survey reports 
having seen sotol in Southern New Mexico with a distinct caudex several 
feet tall, such as some of the Yuccas develop. 
