216 The Plant World. 



sylvatica, and in parts of California the conditions are favorable 

 for their presence, yet no specimens have yet been discovered 

 there. I have indeed seen one specimen of Cladonia rangiferina 

 collected at Seattle, the only Pacific coast locality known to me 

 south of Vancouver. 



The genus Graphis is represented in most temperate regions 

 by the very common species, Graphis scripta, while Graphis 

 elegans is also widely distributed over the eastern United States; 

 yet neither these nor any other species of Graphis is known from 

 California, whereas by analogy one would expect a number of 

 species out of the 400 known. The only representative of the 

 group known is the closely related genus Phaeographis, repre- 

 sented by the species inusta, and it is excessively rare in Cali- 

 fornia. 



Why these Cladonias and Graphis should be absent I can 

 by no means explain, but the presence of lichens common to 

 California and Europe, but not occurring between, can perhaps 

 be explained. The lichens common to Europe and California 

 occur either along the sea coast of California or in the mountains, 

 in regions where the average mean temperature for the warmest 

 months does not exceed 60 degrees Fahrenheit, thus approxi- 

 mating more nearly the life conditions of Europe than do the 

 eastern United States, which have a much higher average summer 

 temperature than the cold and humid regions of Europe lying far 

 to the northward. The humidity of California is for the most part 

 low, but this arid condition is in part compensated by the low aver- 

 age temperature for the summer months, though lying in the same 

 latitude as the eastern states. This cool temperate climate 

 characteristic of California I have elsewhere discussed more 

 fully, and I believe it the most important factor in the determina- 

 tion of the distribution of the species mentioned. 



No other region in the United States has so large a number 

 of lichens which occur nowhere else, so far as known, as has 

 California. Without entering into particulars we may safely 

 place this number at not less than 100; Tuckerman alone de- 

 scribed some 65 new species from California; Nylander, Stizen- 

 berger, and Zahlbruckner together somewhere between 60 and 

 75, while various other authors, including the writer, have described 

 some 20 or 25 additional species. A considerable number of these 



