8 BOTANICAL FEATURES OF NORTH AMERICAN DESERTS. 
cipitation being 45 inches. The country may be considered as an exten- 
sion of the Coastal Plain, with sand ridges higher than at Orange and with 
well-defined drainage channels. The western border of the Atlantic type 
of continuous forest is to be found in this region; also of the southern pine. 
Coastal prairie areas are included, bearing wet-soil grasses, rushes, sedges, 
and many prairie annuals. Marshes are found in which occur the spider 
lily and Daubentia longtfolta. 
Luling, 260 miles west of Orange, is 416 feet above sea-level and has an 
annual precipitation of about 33 inches. The region has a rolling surface, 
the soils being sandy loam, gravelly clay, and rich alluvial bottom-lands, 
and shows many wide expanses of grass-land with an abundance of 
prairie annuals. 
Numerous sandy and gravelly soil species are found, among which are 
Indigofera leptosepala, Crusea allococca, Callirhoe involucrata, Mertolix 
serrulata, Aphanostephus arkansanus, Sida lindhermert, Alhionia nycta- 
ginea, Berlandiera lyrata, and several species of cacti; e. g., Opuntia 
lindheimert, O. leptocaulis, Echinocereus cespitosus, and Cactus heydert. 
San Antonio is 316 miles west of Orange, at an elevation of 686 feet, 
and has an annual precipitation of about 29 inches. This place marks 
with fair distinctness the inner border of the Rio Grande plain, with 
slightly rolling surface and deep porous soils, and the southern margin 
of the Great Plains area, with the roughly eroded escarpment of the 
Edwards Plateau limestone. 
On the one hand, Gulfward, the Rio Grande plain contains a thor- 
oughly lower Sonoran flora, of which woody species are the most obvious, 
constituting the widely known chaparral, which here, however, is scarcely 
typical, being of too luxuriant growth; e. g., the mesquite, which is most 
abundant, being a tree 15 to 20 feet tall. The Mimose begin to dom- 
inate here, notably mesquite, Acacia farnesiana, A. wrighti1, A. amentacea; 
brasil, Zizyphus; much Opuntia engelmanni and O. leptocaulis, Lippia 
(Aloysia) ligustrina, all of which become more abundant west of the 
Sabinal; grasses of the western plains and more of the northern plains 
annuals; Yucca rupicola and treculeana. On the other hand are the 
limestone hills, marking the dissected margin of the Great Plains region 
in a xerophytic timber vegetation with extensive cedar brakes (/un- 
tperus sabinotdes), mountain forms of live-oak and hackberry, shin-oak 
(Quercus breviloba), cedar-elm (Ulmus crassifolia), Ungnadia speciosa, 
Brayodendron texanum, etc., being notably a timber vegetation with modi- 
fied Atlantic forest species mixed with typical lower (and sometimes 
upper) Sonoran species; e. g., madrofia (Arbutus xalapensis). 
Spofford (Fort Clark) is 449 miles west of Orange, at an elevation of 
1,015 feet and with an annual precipitation of 24 inches. This is also on 
the northern border of the Rio Grande plain, and is characterized by 
rolling gravelly ridges and intervening flats with finer soils. 
