270 BOTANICAL GAZETTE | OCTOBER 
CHAPARRAL FORMATIONS, 
The term chaparral as here employed is designed to carry 
with it not merely the idea of a shrubby formation as opposed 
to an arborescent one, but also a formation occupying a specific 
relation to ecological factors. It is a woody vegetation of warm 
temperate or semi-tropical requirements ; adjusted to hydro- 
meteoric conditions wherein there is a minimum of rainfall, a 
dry air subject to regularly recurring movements of great 
velocity, and a high percentage of days of intense sunshine; 
related to edaphic factors in which the soil (waiving its possible 
great fertility or the fact that it may have had a flood débris 
origin) has the loose, shifting, uncohesive quality of soils formed 
by dry weathering and destitute of vegetable mould, if not 
gravelly or stony: and where the soil water level is too deep to 
be available for any but perennial plants with far reaching roots. 
Such conditions of course dwarf the growth of any woody plant 
subjected to them, even if it could endure them at all. Chap- 
arral is the product of such conditions, and while characteristi- 
cally shrubby, many species may under other conditions attain 
to arborescent size, never of course becoming large trees. 
There are two general types of chaparral formation in the 
West Texas region, differing both floristically and ecologically. 
One is the chaparral of the Rio Grande plain, the other that of 
the trans-Pecos region. The difference between these two 
formations is due primarily to the climatic differences between 
the two provinces, and secondarily to differences in geologic and 
physiographic conditions. 
Tue Rio GRANDE CHAPARRAL.— This formation is typically 
a low, more or less impenetrable bush vegetation, covering con- 
tinuously vast areas, and varying in height from two or three 
feet to ten or fifteen, according to varying ecological conditions. 
In the former case, the habitually shrubby and more xerophytic 
species prevail, for example within twenty miles of the Rio 
Grande from Del Rio to Laredo; in the latter, the larger species 
of Mimoseae form the main body of the formation, notably 
Prosopis juliflora as found from San Antonio to Kenedy. No 
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