Apr., 1921] 
HANSON — MALVACEAE IN TEXAS 
197 
parts than near the Gulf. The Rio Grande flows through a broad, some- 
times terraced, valley from Del Rio to the Gulf. Elevation: From about 
ICQ feet where the area borders the Gulf Coast Plain to about 1,000 feet 
at the Balcones Escarpment; at Del Rio 952 feet, at San Antonio 701 feet, 
at Eagle Pass 800 feet. Rainfall: The annual mean ranges from 20 to 25 
inches over most of the area; Del Rio 21.0 inches, San Antonio 26.8 inches, 
Eagle Pass 20.9 inches. Temperature: The mean annual temperature 
at Del Rio is 69.6° P., at San Antonio 70.3° P., at Eagle Pass 71.1° F. and 
from Laredo to the Gulf 73.0° F. Clear Days: The percentage of clear 
days in 1918 at Del Rio was 57.0, at San Antonio 50.9, at Eagle Pass 50.9. 
Humidity: According to Hill, the mean annual evaporation from Rio 
Grande City to Eagle Pass is 50-60 inches, from Eagle Pass to Del Rio 
60-65 inches. 
On the level plains mesquite is dominant. Other important species 
associated with it are Condalia obovata, huisache in the moister areas, 
Quercus virginiana, and others. Grasses and many herbs of tropical 
affinities characterize the sandy plains in the southeastern part. Great 
Plains grasses and herbaceous species are common in the northwestern 
part. On the dry hills and ridges, prominent chaparral plants are Covillea 
tridentata, Acacia spp., Parkinsonia texana, and Leucophyllum texanum. 
The great variety of cacti and yuccas in the westerh part of the region indi- 
cates a greater degree of xerophytism. Along the Rio Grande hackberries, 
hickories, elms, sycamores, and huisaches are conspicuous. 
Abutilon incanum was found frequently in this region in the woods 
along the Rio Grande, in mesquite chaparral on the plains, on rocky and 
gravelly hills, and as a weed along roads. A. berlandieri was rare in the 
woods along the Rio Grande and in mesquite woods along creeks. A. 
wrightii was frequent on rocky hillsides. Callirrhoe digitata was abundant 
in mesquite chaparral in the vicinity of Del Rio and San Antonio. C. 
involucrata occurred frequently in grassy valleys and plains from Laredo 
west and north. C. lineariloba was found only on the sandy, grassy plains 
in the vicinity of Hebronville. Gay aides crispum grew abundantly on 
exposed rocky slopes, mesquite-covered clay slopes, and stream banks in 
the vicinity of Laredo and westward. Hibiscus cardiophyllus was fre- 
quently found in mesquite chaparral on clay hills, on sand and gravel hills, 
and on rocky cliffs along the Rio Grande as far west as the vicinity of Del 
Rio. H. coulteri was found frequently on rocky hillsides along the Rio 
Grande in the vicinity of Del Rio. The region about Del Rio appears to 
be the eastern limit of H. cardiophyllus. Malvastrum americanum occurred 
frequently as a weed in towns and fields and in woods in valleys. Mal- 
vaviscus drummondii was very abundant in the mesquite woods along streams 
in the vicinity of San Antonio, but rare in the Rio Grande Valley. Modiola 
caroliniana was found infrequently as a weed in low, moist places in the 
vicinity of San Antonio. Malva parviflora was a very common and abun- 
dant weed in waste places throughout the region. Sida cuneifolia was 
found commonly in the sandy plain and on sandy hills from Hebronville to 
