334 FOUNDATIONS OF BOTANY 
8. The Pacific Highland Region. — This includes the 
Rocky Mountains, the Sierra Nevada, and the various 
plateaus between them. 
4. The Pacific Slope. — This extends from the Cascade 
Range and the Sierra Nevada to the sea. 
403. Characteristics of the Four Regions. — The forest 
region is mainly remarkable for its great variety of hard- 
wood trees, of which it contains a larger number of 
useful species than any equal area of the earth with a 
temperate climate. In the northeasterly portion and in 
much of the southerly portion there are extensive forests 
of the cone-bearing evergreens, such as pines, spruces, 
hemlocks, and cedars. The vegetation is in general 
such as thrives in medium conditions as regards heat 
and rainfall. 
The plains region is largely dolvoned with grasses, many 
of them xerophytes. Some of the most characteristic plants 
associated with the grasses are Composite, Such as sun- 
flowers, rosin-weeds (Silphium), cone-flowers, gum-weeds 
(Grindelia), and blazing-stars (Liatris). 
The Pacific highland region includes a very great vari- 
ety of plant societies, from the heavily wooded mountain 
slopes and valleys to high sterile plains which are almost 
deserts. Cone-bearing evergreen trees are very character- 
istic of the forests. Great numbers of alpine species of 
herbs and shrubs are found on the mountains at and above 
the timber line. In the alkali regions, where the soil is’ 
too full of mineral salts to permit ordinary plants to grow, 
many kinds of xerophytes, such as the salty sage (Atriplez) 
and the greasewood (Sarcobatus), occur. In the southern 
portion cactuses abound. | 
