290 BOTANICAL GAZETTE | OCTOBER 
plant formations, though exactly the reverse of the preceding 
discussion, namely, in destroying the woody vegetation of cer- 
tain areas. The great demand for charcoal, fuel, posts, and 
rough construction timber, and the desire to secure small patches 
for temporary cultivation are resulting in a rapid removal of the 
xerophytic timber vegetation and the cafion timber from the hill 
country of the Edward’s plateau. This brings up the question 
of the relation of this timber vegetation to the water supply, to 
soil erosion, and to destructive floods. In some cases, at least, 
this formation is succeeded by the rock vegetation and the adobe 
vegetation of the Cretaceous areas, which establish themselves 
as a result of denudation by erosion which follows removal of 
the timber covering. 
SUMMARY. 
1. By reason of its geographic extent and position and of its 
relief, the west Texas region possesses floral elements ranging in 
their temperature relation from tropical to transition. 
2. In its climatic relations the region falls partly under the 
eastern or Atlantic type (Gulf type, Great plains type), and 
partly under the Pacific (Yuma type, Mexican type). This brings 
about great diversity of vegetation in the moisture relation. 
3. This region is the meeting ground of the following floral 
elements: (1) the Gulf neotropical; (2) the Mexican semitrop- 
ical; (3) the Austro-riparian and Carolinian; (4) the Great plains 
upper Sonoran; (5) the north central prairie region; (6) the 
Rocky mountain; (7) the south plateau (of the Rocky moun- 
tains) upper Sonoran; (8) the arid plateau and bolson desert 
lower Sonoran. 
4. The physiographic and geologic provinces coincide _ 
general with vegetation provinces distinguished by characteristic 
vegetation formations. 
5. The flora of the entire region is one of xerophytic aspect, 
but of several grades from semi-arid to extremely arid. Broad 
streamways and cafions and high mountains carry mesophytic 
vegetation into the heart of the region. 
