210 BOTANICAL GAZETTE [ SEPTEMBER 
abundant young vegetation of these prairie annuals. Thus the 
“tallow weeds” (Actinella linearifolia and Amblyolepis setigera), 
which cover many miles of range, are much prized. Not only 
does this annual vegetation sweep as a wave over the prairie in the 
early spring, but the individual species mass themselves in pure 
formations of incredible compactness and extent (fig.7g). Thus 
there may be successive waves of species. In harmony with the 
adaptation which leads to the massing of the species is the fact 
of the brilliance of floral display. This results in vast sheets of 
color. During the spring of 1900, which was unusually favorable 
for vegetation, the virgin prairie plains of Texas were literally 
a sea of color. In his survey of the Rio Grande plain during 
May, Vernon Bailey noted over twenty species which, as he 
expressed it, either occupied exclusively ‘‘acres of prairie” of 
“made miles of solid color.” This was the case in the lower Rio 
Grande country (Corpus Christi to Brownsville) previous to 
May 10. The season of display ended about four weeks later 
on the northern boundary. At Austin by the first of July (often 
even two weeks earlier) a solid grass formation occupies the 
ground which had just previously been exclusively occupied by 
the “blue bonnet” (Lupinus subcarnosus). The continuity of 
grass formation seems in no wise disturbed by the periodical 
dominance of the annuals. 
The species of these formations are of course dependent 
upon seed for their recurrence, and consequently are subject 
wholly to the caprice of rainfall during March and early April. 
When, as frequently happens, there is no rainfall of consequence 
during this period, the display of prairie annuals is very much 
reduced. Their adaptations are in the direction of seasonal 
adjustment rather than toward meeting xerophytic conditions. 
Il. WOODY VEGETATION. 
Since the region under discussion includes only so much of 
Texas as is marked by a distinctly xerophytic vegetation, it 
follows that, except for river bottom and sheltered cafion timber, 
the woody vegetation is as a whole one of xerophytic aspect. 
