346 SYSTEMATIC 



Shetlands, South Orkneys, Tierra del Fuego, South Georgia and the Falkland 

 Islands. During the Glacial period, the polar forms must have spread with 

 the advancing cold ; as the snow and ice retreated, these forms have been 

 left, as already stated, on the higher colder grounds, and representatives of 

 polar species are thus to be found very far from their original haunts. There 

 are few exclusively boreal genera: the same types occur at the Poles as in 

 the higher subtemperate zones. ,One of the most definitely polar species, 

 for instance, Usnea {Neuropogon) -inelaxantha grows in the whole Arctic zone, 

 and, in the Antarctic, is more luxuriant than any other lichen, but it has also 

 been recorded from the Andes in Chili, Bolivia and Peru, and from New 

 Zealand (South Island). 



Cold winds are a great feature of both poles, and the lichens that by 

 structure or habit can withstand these are the most numerous ; those that 

 have a stout cortical layer are able to resist the low temperatures, or those 

 that grow in tufts and thus secure mutual protection. In Arctic and Subarctic 

 regions, 495 lichens have been recorded, most of them crustaceous. Among 

 the larger forms the most frequently met are certain species of Peltigera, 

 Parnielia, Gyrophora, Cetraria, Cladonia, Stereocaulon and Alectoria. Among 

 smaller species Lecanora tartarea spreads everywhere, especially over other 

 vegetation, Lecanora varia reaches the farthest limits to which wood, on 

 which it grows, has drifted, and several species of Placodium occur con- 

 stantly, though not in such great abundance. Over the rocks spread also 

 many crustaceous Lecideaceae too numerous to mention, one of the most 

 striking being the cosmopolitan Rhizocarpon geographicum. 



Wainio' has described the lichens collected by Almquist at Pitlekai in 

 N.E. Siberia just on the borders of the Arctic Circle, and he gives a vivid 

 account of the general topography. The snow lies on the ground till June 

 and falls again in September, but many lichens succeed in growing and 

 fruiting. It is a region of tundra and sand, strewn more or less with stones. 

 Most of the sand is bare of all vegetation; but where mosses, etc., have 

 gained a footing, there are also a fair number of lichens: Lecanora tartarea, 

 Psoroma hypnorum, with Lecideae, Parmeliae, Cladoniae, Stereocaulon alpinum, 

 Solorina crocea, Sphaerophorus globosus, Alectoria nigricans and Gyrophora 

 proboscidea. Some granite rocks in that neighbourhood rise to a height of 

 200 ft., and though bare of vegetation on the north side, yet, in sheltered 

 nooks, several species are to be found. Stunted bushes- of willow grow 

 here and there, and on these occur always the same species: Placodium 

 ferrugineum, Rinodina archaea, Buellia myriocarpa and Arthopyrenia puncti- 

 formis. Some species such as Sphaerophorus globosus, Dactylina arctica 

 (a purely Arctic genus and species) and Thamnolia vermicularis are so 

 abundant that they bulk as largely as other better represented genera such 



' Wainio 1909. 



