LIFE ZONES 461 



(3) Middle Sonoran Zone. This combines the 

 crops of the Upper Sonoran with many of 

 the wild plants and animals of the lower 

 Sonoran. It is subject to severe frosts in 

 winter and spring, rendering it quite un- 

 suited to the orange, olive, and other Lower 

 Sonoran fruit trees. The native trees 

 and shrubby plants delay coming into 

 leaf and flower, notwithstanding the warm 

 days, and so escape injury. The cul- 

 tivated plants, coming from other regions, 

 have not developed this peculiarity. 

 Southern New Mexico is typical of this 

 zone. 

 D. LOWER AUSTRAL. Lower 



(a) East of the Hundredth Meridian. Austral 



(1) Austro-riparian Area. This is the cotton 



belt, occupying most of the Southern 

 states. From it may be separated the 

 following : 



(2) Semitropical or Gulf Strip. Along the coast 



from Texas to Florida ; the region of the 

 palmetto and the sugar cane. 



(b) West of the Hundredth Meridian. 



(3) Lower Sonoran Zone. The desert region of 



the extreme Southwest, characterized by 

 mesquite, cactus, yucca, and many other 

 peculiar plants, as well as a remarkable Tropical 

 set of animals. There is a flora of "winter 

 annuals," appearing in late winter and 

 early spring, and rapidly going to seed. 

 The cultivated trees, of course irrigated, 

 include the date palm, orange, olive, 

 walnut, peach, etc, 



