112 BOTANICAL GAZETTE [AUGUST 
air of very effective velocity, especially during the most active 
growing season. The average velocity per hour for the Gulf 
coast at Port Lavaca (observations taken formerly at Indianola) 
from January to July is fourteen miles, at Fort Elliott in the 
Panhandle 13.4 miles, at Abilene in the central plains province 
11.9 miles. The prevailing direction in these cases, and for all 
the area east of the Staked plains and the Pecos river, is from 
the southeast, except for Fort Elliott, where the winds during 
January, February, and March are from the northwest (of little 
significance as they precede the season of growth). On the 
summit of the plains the velocity is even higher, and the pre- 
vailing direction during the growth period is from the southwest 
and west. The winds of trans-Pecos Texas are also prevailingly 
southwest, so that for the Staked plains and trans-Pecos Texas 
the winds are relieved of their moisture by long passage over 
arid plateau country. East of the Staked plains and of the 
Pecos the prevailing wind is from the Gulf. 
The significance of these winds for plant life is as follows: 
(1) in their mechanical impact upon plants; (2) im rapidly car- 
rying away moisture; (3) in erosion and transportation of soils; 
(4) in moisture-bearing capacity. As to the first point, the 
result is to dwarf and minimize arborescent growth, and to 
exclude plants with broad foliage, or herbaceous plants of tall 
growth. Trees on the coast prairie always incline strongly to 
the northwest, as does also the prairie mesquite in the Abilene 
country. On the summit of the plains, even with irrigation, 
groves of trees are very difficult to start because of the whipping, 
and bruising, and breaking of young branches and foliage by 
the wind. On the coast prairie windbreaks are essential in culti- 
vating orchards. At Alvin the orchards where unprotected by 
windbreaks dwindle away toward the southeast exposure. 
As the final effect of high wind is to promote rapid transpi- 
ration, this danger results in plants with sparse foliage of small 
sized leaves. This is brought about also by prevalent or frequent 
extremes of aridity due to intense heat and lack of precipitation 
throughout the region of high wind velocity. 
