THE FLORAL FEATURES OF CALIFORNIA 23 



from the south through the desert and Great Basin regions following 

 increased aridity. The great Mexican Plateau was the original home 

 of most of the strictly American genera now found throughout arid 

 and semiarid western America. On this plateau a drought-resisting 

 flora existed in the Miocene age, when the greater part of the United 

 States from the Atlantic to the Pacific was covered with a rich decidu- 

 ous forest, comprising such trees as the beach, elm and magnolia — a 

 tvpe of flora that still persists in the southern Atlantic States. 



The role played by climate in California has augmented that of 

 isolation. Without its peculiarities and diversities the rich and varied 

 California flora would never have been evolved. California climate is 

 lauded the- world over. Yet the term means little and is misleading 

 as it carries the impression of uniform climate. Naturally within a 

 state extending through more than nine degrees of latitude, 769 miles, 

 one would expect to find considerable difference in the temperature of 

 the northern and southern sections, with a corresponding difference in- 

 vegetation. But add to this range of latitude diversity of topography 

 with its marked influence on rainfall, temperature and atmospheric 

 humidity, and we have a complexity of climates and climatic influences 

 that are astounding — literally scores of climates sufficiently distinct to 

 influence profoundly the character of the vegetation. 



Temperature, one of the most important factors governing plant 

 distribution, ranges from the perpetual snow fields of the mountains to 

 subtropical valleys where killing frosts are scarcely known. Bordering 

 the snows of the high Sierra such boreal plants as the dwarf, arctic 

 willow, cassiope, bryanthus, primulas and fringed gentians, flourish, 

 while in the subtropical sections, the lime, the olive and the pomegranate 

 are grown, and even the more sensitive though less poetic banana and 

 alligator pear. Everywhere the African pelargoniums, the "geranium" 

 cherished by the eastern housewife and tenderly nurtured within her 

 furnace-heated house, runs riot, growing into good-sized shrubs and fre- 

 quently used for porch coverings or hedges. The castor bean, described 

 in all botanical text-books as an annual, here becomes a tree living for 

 years, and grown for ornament and shade. Between these two extremes 

 boreal and subtropical, are all "the intermediate zones; the cool tem- 

 perate, where rye, red currants and apples flourish, and the warm tem- 

 perate with the almond, apricot and fig. 



But great as is the range of temperature and its effect on vegetation, 

 rainfall and atmospheric humidity are fully as varied and play even a 

 more important role over a large part of the state in determining the 

 character of the vegetation. The normal annual rainfall in certain 

 localities of the northwest coast region runs nearly to one hundred 

 inches. At San Diego, also on the coast, it is only a little over nine 

 inches. On the deserts, lying east of the mountains which have robbed 



