266 BOTANICAL GAZETTE | ocTOBER 
meridians, that is the transition from mesophytic to xerophytic 
zones, is often called the live oak belt because of the character- 
istic occurrence of Quercus Virginiana. The live oak formation of 
the central erosion area has already been described. This is in 
reality a part of the live oak belt, but the characteristic occur- 
rence of the live oak throughout its zone is upon the open grass 
plains of the central region from the Gulf to Red river. 
It occurs in so open and irregular a manner as barely to 
deserve the name of formation. It is in reality a punctuating 
feature in a pure grass plain formation. The occurrence is in 
small isolated clumps whose ecology is that during the first 
years of growth a successful struggle against grazing animals 
and other encroaching agencies is best waged from these com- 
pact masses, which themselves come to have the form of crown 
and individuality of a single tree. These clumps may be called 
centers of infection, for by them the species is spreading. Some 
exceptions to the very open formation occur, as in Live Oak and 
Bee counties, where the live oak timber becomes a very promi- 
nent feature of the landscape. 
The species in this zone is very hardy, and attains a great 
age and large growth. The characteristic growth is expressed 
in the following dimensions, which though far above the average 
as to actual size are by no means unusual; diameter of trunk 
four feet ; height of trunk to main branches six to eight feet; 
total height of tree thirty to forty feet ; spread of crown one 
hundred feet. 
MESOPHYTIC FOREST FORMATIONS OF THE STREAMWAYS.— I here 
are two general types of this formation, namely that of the open 
streamways or broader alluvial river valleys, and that of the 
enclosed box cafions of the erosion areas. 
Timber formations of open streamways.—\t happens that, 
excepting the Rio Grande and Nuéces, the larger rivers rise in 
regions of very low rainfall, and lead into zones of greater 
(often heavy) rainfall. It happens, also, that the direction of 
flow brings them within or accessible to the east Texas forest 
belt. The result is that the streamways are lines along which 
