ae 
Igor] VEGETATION OF WESTERN TEXAS 197 
that the dominant species here are not dominant ones on the 
more western plains. In brief, the ecological type known as 
prairie grasses exists here, as distinguished from the high plains 
type. 
The grass vegetation of the Grand prairie is accompanied by 
avery abundant vegetation of prairie annuals and herbaceous 
Fic, 7.—Rio Grande chaparral at Laredo: sage (Leucophyllum), “all thorn” 
(Rocneicies Mexican persimmon (Diospyros Texanum), and eight or ten other 
species 
perennials, with lignescent, tuberous, or bulbous underground 
parts. These assist in giving the province individuality as a 
grass formation. 
formations of prairie annuals—Since the most conspicuous 
formations of this kind occur in other provinces, this type will 
be discussed later under a separate heading. 
Chalk soil formation of herbaceous perennials.—The species asso- 
ciated in this formation number perhaps thirty-five or forty. It 
occurs throughout the province on the thinnest soils, but comes 
