116 BOTANICAL GAZETTE [AUGUST 
and mesas scattered all over the central prairie provinces. The 
process of leveling is in various stages in different places, such 
as deep dissections in the southern half of the Edwards plateau, 
undulating prairie in the Grand prairie province, a flat plain in 
the granite area with rugose surface caused by projecting granite 
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Fic. 6.— Vegetation provinces of the west Texas region, chiefly on the basis of 
pploniasts and geology: 7 to 74, Rio Grande plain, ae region (7, cee 
mber province; 2@ Edwards plateau plains, grass formations; 26 Grand prairie 
transition, between Lower Sonoran and Austro- -riparian, grass Ens lea. adobe 
vegetation, butte and escarpment timber; 2c, post oak formation on granite, Carbon- 
iferous, and upper cross timber sands and gravel; 2d, grass prairie formations of 
Red beds province, Lower Sonoran with elements of Upper Sonoran; 2¢, erosion 
remnants (buttes) of Staked plains and Cretaceous area, xerophytic timber; ey, 
Staked plains Lower Sonoran; 2g, Staked plains Upper Sonoran ; 24, Toya ah basin, 
f 
belts); 3 to 34, provinces of Rocky mountains and south plateau slope (7, extreme 
Lower Sonoran, bolsoa flora, chaparral, Yucca- -Agave-Cactus formations ; 74, UppeT 
Sonoran ; 34, Rocky mountain transition). 
