SURVIVAL OF LICHENS DURING THE GLACIAL AGE 235 



north during the last Glacial Age only. The dispersal of our species over longer 

 distances is limited. Apart from that, there were, after previous heavier glacia- 

 tions, between Scandinavia and the Riesengebirge probably few suitable 

 habitats for saxicolous species, so it could be assumed that its immigration into 

 Czechoslovakia had already occurred during Mindel time (Cernohorsky, 1961). 



Obviously Parmelia centrifuga is a very old type which has great ecological 

 amplitude. In spite of the fact that the climatic conditions during the Glacial 

 Ages in arctic and central Europe (especially below the firn line) were sub- 

 stantially different, I suppose that the inability of this species to occupy new 

 localities, particularly on the northern and southern limits of its area, con- 

 firms Lynge's conclusion. 



Later Dahl (1946, 1950), a close collaborator of the late Professor Lynge, 

 tried to solve the survival question of the North Atlantic lichens during the 

 Glacial Ages. His method was based on a much broader scale, which he 

 further extended in his later works (Dahl, 1954, 1955, 1958). 



In his first paper Dahl (1946) sketches the history of the Arctic-Alpine 

 flora in Scandinavia from the Last Interglacial. During the Last Glacial Age 

 the central part of Scandinavia was covered by ice, but unglaciated refugia 

 existed in limited spots on the western and northern coasts. Some of the 

 species survived the Last Glacial Age there, and after the retreat of the ice 

 they migrated up into the mountains. Later, in the mountains, they met with 

 other species which had penetrated to this region following the retreating ice 

 from the south and east. The present Arctic-Alpine flora in Scandinavia is 

 therefore a mixture of these two elements. Further, he describes the history 

 even more precisely. He collects proofs to show the unglaciated refugia in the 

 Northern Hemisphere during the Last Glacial Age. Then he distinguishes 

 these refugia into two types: (a) the coastal mountain type (with high 

 mountains near the border of deep oceans) that is further divided into two 

 subtypes: (aa) the Scandinavian subtype — firn line never descends to sea 

 level, Atlantic chmate, rich vegetation of vascular plants, mosses and lichens; 

 (ab) the Antarctic subtype — firn fine descends to the level of the sea during the 

 severest period, Antarctic cUmate, few or no vascular plants, few mosses, rich 

 vegetation of lichens, especially microlichens ; (b) the tundra type (with a 

 continental climate, firn line never descends to sea level, rich vegetation of 

 vascular plants, mosses and lichens). Refugia of the first type (Scandinavian 

 subtype) are found in western and northwestern Scandinavia, probably in 

 Scotland, Iceland, southern Greenland, and possibly Labrador; refugia of 

 the second type in Siberia, possibly in the Kola peninsula, in Novaya Zemlya, 

 northern Norway, Bear Island, Spitsbergen, northern Greenland, and Arctic 

 Canada. The following Arctic-Alpine Hchens are characteristic for the coastal 

 mountain refugia (Scandinavian subtype): Thyrea radiata (Smft.) Zahlbr., 

 Agyrophora rigida (Du Rietz) Llano, UmbUicaria havaasii Llano, and Alec- 

 toria nitidula (Th. Fr.) Vain. Dahl regards these macrolichen species as typical 



