196 
AMERICAN JOURNAL OF BOTANY 
[Vol. 8 
dantly in this region on sandy ridges near Point Isabel. One plant of a 
form of Sphaeralcea lohata was found in a vacant yard near Brownsville, 
No other specimens of this western species were found east of the Pecos 
River. Wissadula lozani was common in open woods and as a weed along 
roads in the vicinity of Corpus Christi and from Brownsville westward. 
W. periplocifolia was found abundantly in openings and along the edges of 
palm woods, and frequently in other woods in the vicinity of Brownsville 
only. 
II. AUSTRORIPARIAN DIVISION OF THE LoWER AuSTRAL 
Area: The part of Texas east of the 98th meridian and north of the 
Semi-tropical Gulf Strip. Topography: Chiefly prairie, low rolling hills in 
places. Soil: The soil varies considerably from sand to clay. There are 
large areas composed of heavy, black clay soil. Elevation: From about* 
100 feet in the southern part to about 1000 feet in the northwestern part; 
at College Station 308 feet, at Dallas 512 feet. Rainfall: The annual mean 
in the eastern part is over 50 inches, in the western part about 35 inches; 
the annual mean at College Station is 37.5 inches, at Dallas 38.0 inches. 
Temperature: The mean annual tCxTiperature at College Station is 67.9° F., 
at Dallas 66.4° F. Clear Days: The percentage of clear days in 1918 at 
College Station was 34.3, at Dallas 44.7. Humidity: The evaporation 
from a free-water surface, according to Hill, is less than 50 inches annually 
for the division. 
As only one locality, the vicinity of Hearne in the southern part of this 
section, was scouted, no attempt is made at listing all the malvaceous species 
that occur in the entire section. The low, red, sandy clay hills in the vicinity 
of Hearne are covered with oak forest, and the wide river bottom of the 
Little Brazos River, consisting of black clay loam, supports a forest of 
hickories, oaks, magnolias, elms, sycamores, and others. 
Malvaviscus drummondii was found commonly, but not abundantly, in 
the bottom-land forest and in thickets on the borders of this forest. Cal- 
lirrhoe involucrata occurred abundantly and commonly in woods, in waste 
places, along roads, and in clearings in this locality. Sida diffusa was very 
rare as a weed in waste places. Modiola caroliniana occurred very com- 
monly and abundantly as a weed in low, moist waste places. The largest 
and best developed Modiola plants found in Texas were in Hearne. 
III. Lower Sonoran Division of the Lower Austral 
A. The Rio Grande Plain 
Area: The Rio Grande Plain comprises the area bounded by the Gulf 
Coast Strip, by the Rio Grande, and by a line drawn from Del Rio to San 
Antonio to the Gulf Coast Strip near Corpus Christi. It is separated from 
the Great Plains to the north, between San Antonio and Del Rio, by the 
Balcones Fault Escarpment. The rocks north of this escarpment were 
lifted up relatively to those south of it. Topography: Marked by flat silt 
plains, sandy plains, low sandy hills, arid clay hills, and ridges of coarse 
gravel. The surface is more hilly and broken in the western and northern 
