SURVIVAL OF LICHENS DURING THE GLACIAL AGE 239 



even the Greatest Glaciation ! Among them are some especially old types, as 

 for example, Rhizocarpon inarense (Vain.) Vain, (mapped by Runemark, 

 1956). The species with a broad ecological amplitude (or with different 

 ecotypes. unknown to us?) or with new resistent mutations probably also 

 have survived the Greatest Glaciation. In any case, the glaciation caused a 

 limitation of convenient habitats and a strong natural selection, which resulted 

 in decreasing the number of species. On the other hand, it of course did not 

 prevent new taxa from arising. The number of species increased again during 

 the Interglacial ages. In the relatively short Postglacial age a small number of 

 species have penetrated into the North Atlantic zone. Evidently the species 

 have immigrated during the different periods and mainly over land. 



In this connection I would like to finish with the conclusion of one of 

 Dahl's last papers (1958): 



". . . there is little to indicate that species unable to grow above 800 m in South Norway 

 migrated across the Atlantic as more hardy species probably did. 



These observations suggest a climate on the hypothetical land bridge similar to 

 that found in the birch belt in South Norway. Such climate probably did not occur in 

 the region concerned until the Pliocene period and it is concluded that the land 

 bridge existed in the Pliocene. 



Independent geological evidence suggests that a basalt plateau was formed stretching 

 from Scotland to East Greenland in the early Tertiary period and existed as a land 

 area until it was broken up in the Pliocene or perhaps as late as the Pleistocene age." 



REFERENCES 



Ahmadjian, v. (1960). The Lichen association. The Bryologist 63, 250-254. 

 Cernohorsky, Z. (1961). Die Flechte Parmelia centrifuga (L.) Ach. im Bohmerwald. 



PresUa 33, 359-364. 

 Dahl, E. (1946). On different types of unglaciated areas during the Ice Ages and their 



significance to phytogeography. New Phytologist 45, 225-242. 

 Dahl, E. (1950). Studies in the macrolichen flora of South West Greenland. Meckl. oni 



Groenl. 150(2), 1-176. 

 Dahl, E. (1954) Weathered gneisses at the island of Runde, Sunnmore, Western Norway, 



and their geological interpretation. Nytt Mag. Bot. 3, 5-23. 

 Dahl, E. (1955). Biogeographic and geologic indications of unglaciated areas in Scandi- 

 navia during the Glacial Age. Bull. Geol. Soc. Amer. 66, 1499-1519. 

 Dahl, E. (1958). Amfiatlantiske planter. Problems of Amphiatlantic plant distribution. 



Blyttia 16, 93-121. 

 Dahl, E., Lynge B. and Scholander, P. F. (1937). Lichens from Southeast Greenland. 



Skr Svalbard og Ishavet, No. 70, 1-76. 

 Degelius, G. (1957). The epiphytic lichen flora of the birch stands in Iceland. Acta Horti 



Gotoburg. 22 (l), 1-51. 

 Lamb, I. M. (1947). A monograph of the lichen genus Placopsis Nyl. Lilloa 13, 151-288. 

 Llano, G. A. (1950). A Monograph of the Lichen Family Umbilicariaceae in the Western 



Hemisphere. Washington. 

 Lynge, B. (1928). Lichens from Novaya Zemlya. Rep. Sci. Res. Norweg. Exped. Novaya 



Zemlya 192h Oslo, No. 43, 1-229. 

 Lynge, B. (1933). On Dufourea and Dactylina. Three Arctic lichens. Skr. Svalbard og 



Ishavet, Oslo, No. 59, 1-62. 

 Lynge, B. (1934). General results of recent Norwegian research work on Arctic lichens. 



Rhodora 36, 133-171. 



