(,I:M:KAL SI'KVEY OF TEXAS WOODLANDS. 



11 



\Valler Counties nortlu ashvard to Harrison and Red River Counties, 

 where the summer or fall months are driest. The wettest season is 

 spring in the central and eastern portions of the State, and summer in 

 \\Vst Texas and Northwest Texas, the Rio Grande Valley and Coast 

 section, except over a limited area from the lower Rio Grande Valley 

 northeastward to Calhoun County, where fall is the wettest season. The 

 per cent of moisture received during the growing season is least in 

 East Texas and greatest in Northwest Texas, where it is most needed.. 

 In the humid region of the State the annual precipitation is always 

 sufficient to saturate the soil and sub-soil and furnish a constant supply 

 of run-off to the streams. Surface evaporation is retarded by the mantle 



Map 5 Floral Features of Texas. 



1 Atlantic forest belt; 2 Rocky Mountain forest; 3 Chaparral; 4 Black 



Prairie ; 5 Bolspn desert flora ; 6a Grand Prairie ; 6b Great Plains ; 



7 Transitional, with plains, prairie, and Atlantic flora ; 



8 Coast prairies ; x x x x Yucca belts. 



of vegetation and the greater average humidity; also high winds are far 

 less constant. In the more arid portions the conditions are reversed. 

 The rainfall is always local and is seldom sufficient to saturate the sub- 

 soil or to maintain a system of waterways, hence there are extensive 

 areas without visible surface drainage or the streamways are dry during 

 most of the year. Evaporation is facilitated by high winds, absence of 

 humid conditions in the atmosphere and lack of a protecting cover of 

 vegetation. 



The forest types in a general way correspond with the zones of rain- 

 fall. (See Map 5.) In the eastern region where the rainfall exceeds 



