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THE AMERICAN NATURALIST [Vol. XLVI 



In the chaparral may sometimes be seen the magnificent Wash- 

 ington-lily and the stately Humboldt-lily, while under the shade 

 of the great Conifers the vivid crimson Snow-plant (Sarcodes) 

 may often be found. 



Southern California is largely a desert region, the transverse 

 Tehachapi range of mountains shutting it off from the great 

 central valley to the north. The Mojave desert, south of the 

 Tehachapi, is an arid plateau whose scanty vegetation is of a 

 marked xerophytic type. Cacti are abundant and the most 

 striking plants are the tree Yuccas (Y. arborescens) . Other 

 species of Yucca with magnificent panicles of white flowers also 

 occur, flowering in the late spring and early summer. Farther 

 south there are rich valleys opening toward the sea, and less 

 arid than the tableland to the north, and the Colorado desert to 

 the southeast. The latter region, which includes Death Valley, 

 is a desert of the most pronounced type, some of it lying below 

 sea level, and extremely hot and dry. Opening into the Colo- 

 rado desert, however, there are small canons with permanent 

 streams coming down from the lofty mountains, and supporting 

 a more or less mesophytic growth of Cottonwoods, Sycamores 

 and Willows, and in some of the canons there are imposing 

 groves of the stately Washington Palm (W ashing tonia filifera). 

 This southern region is really part of the great Sonoran region 

 of Mexico and its vegetation is essentially the same. 



The remarkable range in conditions often within very short 

 distances, e. g., the eastern and western slopes of the Coast 

 ranges, results in an extraordinary variation in the vegetation 

 within a relatively small distance, and perhaps no equal area in 

 the world, outside the tropics, can show a greater number of spe- 

 cies than California. Moreover, a very large number of these 

 species are endemic and there are also very many peculiar genera. 

 Some of the genera are characterized by a great number of spe- 

 cies. Thus the genus Ribes (see Harshberger, p. 273) is credited 

 with forty species against thirteen for the whole region covered 

 by Britton and Brown's Manual. Other large genera are Calo- 

 chortus, Orthocarpus, Pentstemon, Lupinus, Trifolium, Gilia. 



Professor L. R, Abrams has kindly furnished the writer with 

 some data showing the remarkable endemism of many California 

 genera. Of the forty known species of Ceanothus thirty occur 

 in California, and twenty-five of these are endemic. Sidalcea 

 with a total of nineteen species is represented in California by 



