286 BOTANICAL GAZETTE [OCTOBER 
conditions of the southwest, and occur not only throughout 
that area, but over its southward extension along the conti- 
nental axis south of the equator. Their distribution in the west 
Texas region coincides with the areas of escarpment, and of 
cafion erosion. They occur, for example, throughout the central 
erosion area. Aside from the various means of adapting the 
vegetative plant to xerophytic conditions, the ecological rela- 
tions of this group of ferns has not been much studied. 
Two additional important species are to be noted, namely, 
Selaginella lepidophylla (a ‘“‘resurrection”’ plant) of the trans- 
Pecos region, but also extending eastward on limestone bluffs 
and knobs to the Frio river; and Se/aginella rupestris (the forms 
still so designated) is especially abundant in the granite area, 
but it appears to be in all of the mountainous or hilly areas of 
west Texas (on dry gravel ridges at Austin), on limestone hills 
on the upper Nuéces cafion, and in trans-Pecos mountains. 
Several extremely xerophytic mosses are essentially rock plants. 
Some form close velvety masses on granite and sandstone. 
Other species occur with Selaginella rupestris, and Scytonema, and 
lichen mats on the dry gravel ridges and on compact limestone 
débris. Several xerophytic species of liverworts occur upon 
granite fissures and upon gravelly soils, notably three or four 
species of Ricciaceae, 
HALOPHYTIC VEGETATION. 
The areas in the west Texas region in which the soil is 
impregnated with alkali sufficient to affect the vegetation cover- 
ing are rather large and widely distributed, and have been but 
little investigated from a botanical point of view. There are 
included here in general (1) the gulf coast, (2) basins in the 
lower Rio Grande plain, (3) the gypsum beds of the red beds 
country, (4) the alkali basins of the western side of the Staked 
plains, (5) the Pecos valley or Toyah basin, (6) the bolson 
basins of trans-Pecos Texas of which the Howard and Hueco 
bolsons are the largest. 
From Dr. Havard’s description of the ‘‘ Pecos flats” and of 
