1901] VEGETATION OF WESTERN TEXAS 289 
grasses (Andropogon), often as high as a horse’s back. After 
pasturing and subsequent trampling and hardening of the soil 
the dog grasses or needle grasses took the whole country. After 
further overstocking and trampling the needle grasses were 
driven out and the mesquite grasses (Hilaria and Bulbilis) 
became the most prominent species.” 
There is a further strong tendency toward the establishment 
of a weed vegetation to the disadvantage of what may be called 
the native vegetation. Such for example are Gutierresia Texana 
and Croton Texensts. 
Regarding the establishment of woody vegetation, it is the- 
unanimous testimony of men of long observation that most of 
the chaparral and mesquite covered country was formerly open 
grass prairie. This applied to the Rio Grande plain, as well as 
to the mesquite flats of the central provinces, Illustrations are 
everywhere at hand. At Austin, for example, many black land 
pastures have within a few years become covered by a perfect 
jungle of mesquite. 
Apparently under the open prairie régime the equilibrium 
was maintained by more or less regular recurrence of prairie 
fires. This, of course, is by no means a new idea, but the 
Strength of it lies in the fact that the grass vegetation was toler- 
ant of fires and the woody vegetation was not. It was only 
after weakening the grass floor by heavy pasturing and ceasing 
to ward off the encroaching species by fire that the latter 
invaded the grass lands. Once the equilibrium was destroyed 
everything conspired to hasten the encroachment of chaparral— 
droughts, pasturing, trampling, seed scattering, and so on. As 
Smith pointed out, a mesquite tree once established became a 
center of infection in offering shelter for shrubby plants and 
shade-loving grasses, driving out the native prairie grasses. In 
brief, the efforts to exploit the wealth of grass lands for profit, 
namely stock raising, have been the main agency in transform- 
ing them rapidly into lands covered by a totally different and 
far less valuable vegetation. 
Another economic question arises from artificial change of 
