198 
AMERICAN JOURNAL OF BOTANY 
[Vol. 8 
Laredo. S. angustifolia occurred frequently in valleys and as a weed in 
fields from the Gulf Coast Strip to Laredo and Cotulla. S. diffusa and 
S. filijormis were common on rocky and gravelly hills, on dry clay hills, on 
plains, and in valleys throughout the region. S. hastata occurred commonly 
in valleys, on plains, and on rocky and sandy slopes, and as a weed along 
streets. Sphaeralcea cuspidata was found abundantly in sandy, loamy, 
and clay soil in valleys and as a weed along irrigation ditches and in fields 
from Eagle Pass westward. S. hastidata was abundant on the sandy plain 
and in gravelly places south of Hebronville. 5. pedatifida was frequent 
on sandy and gravelly slopes from Laredo to Cotulla and Eagle Pass. 
B. The Great Plains 
Area: The Great Plains includes the area from the Balcones Fault 
Escarpment between Del Rio and San Antonio west to the mountains in 
Trans-Pecos Texas and northwest throughout Texas. The portions of 
this area below 4,000 feet belong to the Lower vSonoran; the areas above 
4,000 feet belong to the Upper Sonoran. Topography: The southern part is 
dissected into rugged hills and deeply eroded ravines and canyons. The 
area west of the Pecos River is more elevated and rougher than the area 
east of it. The northern part is generally quite flat. Elevation: 1,000 to 
over 4,000 feet; at Junction 2,180 feet, at Barstow 2,573 fe^t* Fort Stock- 
ton 3,050 feet, at Plainview, near Crosbyton, 3,370 feet. Rainfall: For most 
of the area the mean annual precipitation is from 15 to 20 inches. At 
Junction it is 25.1 inches, at Barstow ii.i inches, at Fort Stockton 15. i 
inches, at Crosbyton 21.0 inches. Temperature: The mean annual 
temperature at Junction was 65.4° for 1918, at Barstow 64.5°, at Fort 
Stockton 64.0°, at Crosbyton 59.7°. Clear Days: The percentage of clear 
days at Junction in 1918 was 59.0, at Barstow 64.4, at Fort Stockton 44.2, 
at Crosbyton 59.7. Humidity: The mean annual evaporation, according 
to Hill, ranges from 60 to 80 inches per year throughout the region. 
The southern part of this region is a sparsely wooded area, the northern 
part a short-grass area. Characteristic plants of the southern part are 
mesquite. Acacia spp., Mimosa spp., hackberries, pecan, oaks, pifion 
pine, mountain cedar, Covillea, cacti, yucca, and agaves. The bald cypress 
{Taxodium distichum) finds its western limit in this region. 
Abutilon incanum was found frequently in wooded valleys, in rocky 
ravines, and on rocky slopes from Ozona to Fort Stockton and southward 
through the area. Abutilon wrightii was found frequently on rocky slopes 
and cliffs in the southern part of the region. A. texense was rare in open 
mesquite in valleys from Ozona to the Pecos River, and in the shade of 
mesquites in the depressions on the plains near Barstow. Callirrhoe 
digitata was abundant in thickets along the lower part of the Devils River. 
C. involucrata was common and abundant in woods and in openings in 
valleys from Del Rio to Ozona and Sheffield. Disella lepidota was abundant 
in slight depressions in the plains in the vicinity of Pecos. Gayoides crispum 
was found frequently in rocky situations in the southern part. Hibiscus 
cardiophyllus was rare on rocky banks of the Rio Grande near Del Rio. 
