Origin of California Lichen Flora. 217 



including some of the most remarkable, such as Ramalina reti- 

 culata, extend northward as far as Vancouver, while there is no 

 question that a more extended knowledge of the western lichen 

 flora will show that perhaps half of the great number described 

 from California also occur in some part of the adjacent states. 

 But at present at least 100 have not yet been collected beyond 

 the confines of the state. 



Among these reir.arkable forms we may mention Dendro- 

 grapha leucophaea, and minor, Ramalina menziesii, Schizopelte 

 calif arnica, Caloplaca coralloides, Lecanora phryganitis, Cyphel- 

 iutn bolanderi, Hassea hacillosa, Aneptychia erinacia, Heterocarpon 

 ochroleticum, Buellia oidalea, Platygrapha hypothallina, Schis- 

 matomma pluriloculare, and a host of xerophytic Acarosporas, 

 Endocarpons, Heppias, and the like. 



At least some of the reasons for the remarkable character 

 of California's lichen flora may be considered fairly certain. 

 Among these we are safe in placing the very equable climate, 

 the long dry season from April to October or November, and Cali- 

 fornia's geographic isolation. It is true that California extends 

 over m.ore than nine degrees of latitude, but this has less eff"ect 

 on the character of her lichens than would be supposed. It is 

 likewise true that California has the most varied topography of 

 any state in the union, the highest peak and the deepest valley, 

 but except on the very highest mountains onUn the most barren 

 depths there is relatively but slight variation. The aridity 

 and scant rainfall of most of California south of Pt. Reyes, and 

 the fact that the rain falls only during a few months of the winter, 

 of itself tends to give a strongly xerophytic cast to the general 

 flora, a tendency just as strongl}- evidenced in the lichen flora 

 as well. 



By California's geographic isolation I mean her separation 

 from the rest of the country eastward by the enonnous and 

 towering Sierra Nevada range, beyond which stretches for hun- 

 dreds of leagues an elevated, arid waste or desert plateau, on 

 which for a thousand miles the common lichens of the humid 

 east find little or no lodgment. In southern and southeastern 

 California this desert extends well toward the Pacific, though 

 no longer elevated but indeed passing below sea level, and in- 

 cludes such notorious regions as Death Valley, the Mojave, and 



