a 
1901 VEGETATION OF WESTERN TEXAS 279 
about Austin. In the valley of the Nuéces river, about midway 
of the plain, this Opuntia attains gigantic size, being said to. 
exceed a height of ten feet. In the vast mesquite forest on the 
northeastern border of the Rio Grande country, the prickly pear 
is an undergowth four or five feet high. These two species 
together are practically blocking up large tracts of pasture lands, 
not only changing grazing conditions, but rendering the use of 
such: lands for agricultural purposes an expensive enterprise, 
oe | 
Fic, 21.— Larrea Mexicana (Mexican greasewood) formation; typical bolson 
desert of trans-Pecos Texas; Fouguiera splendems associated here.— Kodak view by 
R. T. Hill, 
This Opuntia fruits regularly and in great quantity, and appar- 
ently is chiefly spread by means of seeds. These have been 
found germinating in great numbers in cow chips. The juicy 
fruits are eaten not only by cattle, but —— by other mam- 
mals as well, and by birds. 
THE CYLINDRICAL OPUNTIAS.—These are chiefly plants of the 
high plains westward, Opuntia frutescens being an exception. This 
Species is part of the chaparral of the Rio Grande plain and the 
adjacent provinces northward. It occurs especially in associa- 
tion with spreading shrubby species by which it partially sup- 
Ports its slender stems, and together forming well-defended 
clumps of chaparral, from which there is a gradual encroachment 
upon the grass formation. The presence of the Opuntia prevents 
the shrubs from being eaten back by cattle. Opuntia arborescens 
