GEOLOGICAL AND GEOGRAPHICAL DISTRIBUTION 549 



much greater. California alone has more species of Conifers than 

 the whole of the United States east of the Rocky Mountains. 



Owing to the dryness of the summer, most of the trees and shrubs 

 in the central and southern parts of the state are markedly xerophytic 

 in character. The evergreen leaves are small and thick, well fitted 

 to endure the hot, dry summer. The great valleys are too dry to 

 allow the growth of forests, but the bottom-lands, and the foot- 

 hills of the moister valleys, are covered with wide-spreading oaks, 

 some of which, like the Live-oak (Quercus agrifolia), are evergreen. 

 The lower mountain slopes and the foot-hills are generally covered 

 with a dense growth of shrubs, sometimes thorny, and always 

 difficult to traverse. This " chaparral " is composed of a variety of 

 shrubs, including species of Oak and Chestnut, but largely composed 

 of species of Ceanothus, Adenostoma, Poison-oak (Bhus diversilobus) 

 and Manzanita (Arctostaphylos). Associated with these are many 

 beautiful bulbous plants like the Washington-lily, Brodisea, Calo- 

 chortus, Zygadenus, etc., which are very largely represented in the 

 California!! flora. 



South of the Tehachapi mountains (lat. 35) the country is much 

 more arid, and much of Southern California, especially the south- 

 eastern part, presents genuine desert conditions. Cacti, Yuccas, 

 Sage-brush, and other characteristic desert plants prevail, and, except 

 when irrigated, the land is quite useless for agriculture. 



Constituents of the California Flora. The position of California, 

 extending for ten degrees of latitude along the Pacific Ocean, and 

 absolutely shut off from communication with the eastern United States 

 by impassable mountains and deserts, has resulted in a flora having 

 but little in common with that of the Atlantic states. While a good 

 many northern plants have made their way southward, following the 

 mountains, few of these reach beyond the middle of the state, where 

 they are mingled with many types quite unlike any eastern forms, 

 and which have undoubtedly been derived from the south. It is 

 from Mexico, and to some degree from western South America, that 

 the characteristic plants of the open dry valleys and hills of middle 

 and southern California originally came, although a very large 

 number of them have become modified into distinct genera and 

 species. The open valleys and low hills in early spring are ablaze 

 with a marvellous variety of brilliant flowers, most of which are 

 quite new to the eastern student. The fiery orange Eschscholtzia, the 

 pure blue Nemophila, the creamy Platystemon, golden Composites in 

 great variety, blue, white, and yellow Lupines, violet Brodiaeas, and 

 parti-colored Calochortus, form wonderful flower-carpets, whose 

 beauty must be seen to be appreciated. 



These flowers, as well as many others, are either quite unrelated 

 to eastern genera or represented only by a small number of forms, 



