Prairie- and Sand Hill District. 529 
of the vegetation. Even in the region of greatest rainfall, however, the climatic 
conditions, together with geologic and physiographic conditions, result in a 
decidediy xerophytic vegetation. The grass vegetation is a direct expression 
of the xerophytic conditions, and certain ecologic types of grasses are found 
through the entire region, as Buchloö dactyloides specifically designated as 
“buffalo grass”. Setting aside the coastal prairies‘) which are sod prairies with 
grasses and sedges of mesophytic requirements and annuals similarly adapted 
to wet, low, coast lands, the prairie plains demand our attention as the southern 
extension of the prairie region proper. 
The prairie plains embrace the grass country of central and north Texas. 
They merge with the prairies in the wooded country to the east and with the 
Great Plains proper (Llano Estacado, Edwards Plateau and Stockton Plateau) on 
the west. The dominant vegetation is a grass formation, but upon the areas 
of sand and gravel exposed an the hills, bluffs and streamways, where the sod 
is not compact, timber formations prevail. Grand Prairie which occupies a 
lower Cretaceous area supports a grass vegetation, accompanied by a very 
abundant assortment of prairie annuals and herbaceous perennials, with lignes- 
cent, tuberous, or bulbous underground parts. The underground parts accor- 
ding to BRAY are several types, as succulent fibrous roots with a thick zone 
of mucilaginous or saponaceous tissue (Krameria secundiflora, Yucca rupicola); 
woody subterranean tuberous caudex Ziatris pycnostachya; mucilaginous bulbs 
with impervious coats (Allium, Cooperia), and deep irregular or fusiform roots 
with hard sclerenchymatous coat (Aslepias decumbens). The plants with these 
characters assist in giving individuality to the grass formation. The Red Beds 
plain?) of reddish chocolate soil, west of the Grand Prairie, shows two specific 
formations constantly to be distinguished, viz: the Hilaria Famesii association 
and the Arzstida fasciculata association which occurs on ridges alternating with 
the lower areas of Aullaria. 
These grasses together with the black grama (Hilaria mutica), curly mesquite grass E. cen- 
chroides) from a fairly close sod in which grow such annuals as Sphaeralcea angustifolia, S. 
cuspidata, Malvastrum coccineum, Gaillardia pinnatifida, Actinella (Tetraneuris) linearifolia, ion 
runeinata, Xanthium texana, Berlandiera lyrata, Polypteris Hookeriana, Hoffmanseggia strieta and 
Mentzelia nuda. 
1) See discussion under head of coastal plain forests where these prairies are referred to. 
The great plains ze extend southward in great strength over the Llano Estacado, the 
plateau country. about Fort Davis, Alpine, Marfa, &c. and are strong over the en . Beds 
country, the ee and Black prairies, and extend in some strength over the black prairie lands 
to the Gulf at Port Lavaca and Corpus Christi. There is further an element which is not 
typically Great Plains, or ” anyrate is a more mesophytic expression of it which or. the 
prairie region in Indian Territory and eastern Kansas and is very strong in the Black and Grand 
Prairies of Texas. from a letter, dated Oct. 28, 1903 from Prof. Wır.Lıam L BrAY, 
University of Tex: 
BrAY, Won ıLLıaM L.: The ecological Relations of the Vegetation of western Texas. 
Botanical Gazette XXXII; 199, Aug., Sept., Oct. 1901. 
Harshberger, Survey N.-America, 34 
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