SURVIVAL OF LICHENS DURING THE GLACIAL AGE 237 



seen, they are often poorly developed and corticated. The dispersal by means 

 of these diaspores may not always be effective : the circumpolar sorediate 

 lichens are usually common, but all the non-circumpolar sorediate species 

 are rare in the Arctic (Lynge, 1934). Because the formation of apothecia (and 

 spores) in many Arctic macrolichens is also limited, they can reproduce only 

 by means of thallus fragments. These latter of course do not permit dispersal 

 over long distances. 



Now I return to the conclusion in Dahl's paper (1946). In it, Dahl solves the 

 problem of the southwest Greenland macrolichen flora and its relation to the 

 Scandinavian one, which it approaches in identity. In his later paper (Dahl, 

 1950) he goes into the same problem, using a rich material. Here he compares 

 the macrolichen flora of southwest Greenland and the macrolichen species in 

 the floras of Scandinavia and central Europe. He states that 24 species are 

 found in southwest Greenland and in Scandinavia, but not in the mountains 

 of central Europe. Analogically there are in Scandinavia 36 species of Alpine 

 lichens which have not been discovered in the mountains of central Europe. 

 The Scandinavian and the central European mountains possess 15 common 

 Alpine macrolichen species. Only 1 1 Alpine species found in the central Euro- 

 pean mountains occur neither in Scandinavia nor in southwest Greenland. 

 Consequently the relation between the macrolichen flora of southwest Green- 

 land and the Alpine macrolichen flora of Scandinavian is closer than the 

 relation between the Alpine macrolichen flora of Scandinavia and that of the 

 central European mountains. Dahl explains the cause of this phenomenon: 

 he supposes, that "(1) the lichen floras of Southwest Greenland and of 

 Scandinavia date from a period when the correspondence in the whole flora 

 between Europe and east America was closer than today. (2) The conditions, 

 under which the lichens in Scandinavia and southwest Greenland had to live 

 during the Last Ice Age, were almost the same in the two districts, but 

 diff'erent from those in other areas like Novaya Zemlya or the Alps" (refugia 

 of the coastal mountain type, the Scandinavian subtype). 



Dahl (he. cit.) came to the first point of his explanation by comparing 

 vascular plants known in Europe only as fossils from Interglacial layers, but 

 still growing today in America. From this he concludes that the flora of 

 Europe during the Last Interglacial probably had a more American character. 

 If this was really the case, then the Arctic-Alpine flora could either survive 

 even the largest glaciation on some refugia in northwest Europe (when 

 several of them in the Northern Hemisphere probably were of the Antarctic 

 type), or else a closer connection existed between northwest Europe and 

 northeast America during the Last Interglacial. 



Later Dahl (1955) returns again to the question of unglaciated refugia in 

 Scandinavia. He devotes his attention exclusively to vascular plants and 

 underlines here the presence of West Arctic species which otherwise are 

 lacking in Europe and west Asia. Further, he points to the endemism in the 



