139 



In a recent paper by Dr. Darblshire* on Arctic flora, a most 

 interesting and enlightening comparison of Arctic species with 

 those of Germany is made, showing that the advance and 

 retreat of the ice age explains a remarkable distribution, which 

 results in 72.3 per cent, of Arctic lichens being found in the Tyrol. 

 A conclusion, that the crustose species are of a later evolutionary 

 development than the fruticose, is also brought forward by means 

 of comparison of the two floras. 



A few examples taken from the Usneaceae show the correlation 

 that I have in mind, and which at a later date I hope to be able 

 to take up in more detail. 



Genus: Usnea 



U. plicata (L.) Web. I have before me examples of Usnea 

 plicata from the Alps which are practically as robust as those 

 from the Californian coast, and are impossible to separate if 

 the labels are withheld. These Californian plants have been 

 described as representing a new species, i. e., U. californica 

 Herre. This species was considered by Dr. Zahlbruckner to 

 belong to the series Pachynae, but in reality it is a Mesinae, a 

 point in which Dr. Zahlbruckner now agrees with the author. f 

 Dr. Herre was perhaps mislead by this belief when he described 

 the species. 



U. articulata (L.) Hoffm. Though this species is never well 

 developed in our area, it is found only on the Californian coast. 

 It is of course a well marked species in the British Isles. 



Genus: Letharia 



L. vulpina (L.) Ach. This plant occurs throughout north- 

 western United States, reaching in California perhaps, a slightly 

 more robust development (i. e., L. vulpina var. californica 

 Nyl. = L. Columbiana Nutt.) and is an exactly parallel case with 

 U. plicata. 



* Rept. 2d Norwegian Arctic Exped. "Fram," 1898-1902, Videns. Sels. I Kxist. 

 Si-53. 1909. 



t In litt. Sept. 9, 1913, "Die californica, deren Originate exemplar bei mir erliegt 

 ist eine echte Pachyna." In litt. Feb. 2, 1914, "Darin haben Sie recht, dass Usnea 

 californica nicht zu des Pachynae gehort." 



