344 A TEXT-BOOK OF BOTANY 



typical one; and the Desert of Sahara is another well-known 

 illustration. 



207. Thickets. Xerophytic thickets are the most 

 strongly developed of all thicket growths. They are spe- 

 cially characteristic of the subtropics, and may be described 

 as scraggy, thorny, and impenetrable. Such thickets are 

 well displayed in Texas, where they are called "chaparral"; 

 and similar thickets in Africa and Australia are spoken of 

 as "bush" or "scrub." In all of these cases the thicket is 

 of the same general type, and is one of the most forbidding 

 areas for travel. 



208. Forests. The most common xerophytic forests of 

 the United States consist of conifers, especially of pines. 

 They occur along the rocky slopes of the mountains, and 

 on the vast sandy areas that border the Great Lakes and 

 cover the Gulf States (Fig. 312). 



209. Salt steppes. In these areas, not only are the 

 drought conditions continuous, but the water is alkaline. 

 The salt steppes are interior dry wastes which probably 

 mark the site of old sea basins. In the United States one 

 of the most extensive of the salt steppes is the Great Salt 

 Lake Basin. Another extensive alkaline waste is known as 

 the Bad Lands, which stretches over certain portions of 

 Nebraska and South Dakota. 



210. Salt and alkaline deserts. In these areas the 

 water-supply is at its lowest ebb, and therefore is saturated 

 with the characteristic salts of the soil. No worse com- 

 bination for plant activity can be imagined than the com- 

 bination of scanty water-supply and abundant salts. In 

 consequence, such areas are almost, if not absolutely, devoid 

 of vegetation. As illustrations, the extensive desert of the 

 Dead Sea region and the Death's Valley in southern Cali- 

 fornia may be cited. 



