334 FOTTNDATIONS OF BOTAIIT 



3. The Pacific Highland Region. — This includes the 

 Rooky 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 covered with grasses, many 

 of them xerophytes. Some of the most characteristic plants 

 associated with the grasses are Compositse, such as sun- 

 flowers, rosin-weeds (Silphium), cone-flowers, gum-weeds 

 (Grrindelia),' and. blazing-stars (Liatria). 



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 [Atriplex) 

 and the greasewood {Sarcohatua), occur. In the southern 

 portion cactuses abound. 



