340 



General Botany 



Fig. 213. Giant cactus and desert shrubs near Tucson, Arizona. 



W. S. Cooper 



rooted cacti. The agaves accumulate water in their fleshy 

 leaves, and the yuccas are deep-rooted. The shrubs for the 

 most part are deep-rooted and live in soils where water flows 

 or seeps from the better-watered mountains and elevations. 

 Northward the succulent desert gives way to the sagebrush 

 semi-desert ; eastward and westward it passes into small-leafed 

 desert scrub. 



All the perennial plants show reduced leaf surfaces. Some 

 have leaves only during the rainy season, and others, like the 

 cacti, are quite devoid of foliage leaves. Heavy cuticles, bloom, 

 and thickened epidermal cells are found on the agaves and yuccas. 



In southern Mexico the desert gives way to semi-desert tropical 

 scrub, which in turn merges into the tropical jungle that occupies 

 more and more of the land through Central America to Panama. 

 On the higher mountains subtropical oak and other hardwood 

 forests pass into pine forests at still higher elevations. The 

 highest peaks reach above timber line and have small areas of 

 alpine vegetation. 



