302 BAILEY: THE WILD COTTON PLANT IN ARIZONA 
subdivision which range over the colder slopes. It does not usually 
occur near the bottoms of canyons but prefers the hottest, dryest 
open slopes or open side gulches in rocky situations. Its range, 
however, is not continuous even in the most favorable parts of 
its own belt, as it occurs only in interrupted areas on each of many 
isolated and widely separated mountain ranges. It is therefore 
especially important to know the more abundant plants with 
continuous ranges which mark its subdivision, so as to know 
where to look for it. , 
FIG. 1 FIG. 2 
Fic. 1. Dasylirion Wheeleri; near Globe, Arizona. November, 1913- 
FiG.2. Thurberia thespesioides; in Sabino Canyon, Santa Catalina Mountains, 
Arizona. October, 1913 
The most conspicuous plant with which Thurberia seems always 
to be associated, is the sotol (Dasylirion Wheeleri). This has the 
same lower limit but runs a little higher and overlaps the lower 
edge of Upper Sonoran zone. The sotol is a very abundant and 
conspicuous plant, fully encircling most of the mountain ranges 
that reach above Lower Sonoran zone. 
Other plants generally associated with Thurberia and marking 
