236 ZDEN^K CERNOHORSKY 



for the tundra refugia: Dactylina arctica (Richards.) Nyl., D. ramulosa 

 (Hook.) Tuck., D. madreporiformis (Wulf.) Tuck., Parmelia subobscura Vain., 

 Omphalodiscus krascheninnikovii (Sav.) Schol., and Cetraria chrysantha 

 Tuck. Before he draws a conclusion, he shows also that some southern species 

 could survive the Last Glacial Age on unglaciated coastal mountain refugia, 

 and the more so the more Atlantic the climate was, for example on the west 

 coast of Scandinavia and especially in the British Isles. 



But Dahl does not enumerate any hchens of this latter type. No doubt, as 

 an example there can be mentioned some of the southern species from 

 southwest Greenland (Dahl, 1950, p. 157-158) and probably even some of the 

 north coast hchens from Svalbard. Placopsis gelicia (L.) Nyl., which forms a 

 transition between macrolichens and microhchens, could probably also be 

 named. This is a species of a more or less pronounced Atlantic (oceanic) 

 nature, the distribution of which was mapped by Lamb (1947). Because it 

 was previously mentioned even from Czechoslovakia, I carefully noted its 

 occurrence in the southwestern part of Iceland in 1948. I collected it there in 

 several low altitude localities, but also on the nunatak of the glacier Thoris- 

 jokuh, 1060 m (with the firn hne above the foot of the nunatak). Therefore 

 we may conclude that it could have survived the Last Glacial Age even in the 

 unglaciated refugia in Iceland. 



Lamb (1947) writes that only the coastal mountain refugia would have 

 been available for it during the Pleistocene age. He supposes that its present 

 extention to Spitsbergen, Bear Island, northernmost Norway, and Novaya 

 Zemlya in the east, and to the Boothia Peninsula of Arctic Canada in the 

 west, must therefore be the result of migration in the Late Glacial and Post- 

 glacial times. This statement may be supported by the fact that soredia of 

 Placopsis gelida are usually present. In this connection I would hke to mention 

 the said specimens from the nunatak Thorisjokull, which, compared with 

 those from the lower locahties of southwestern Iceland, have the whole 

 thallus sorediate. It seems that this phenomenon is a reaction of the plant to 

 external factors. Also Lynge (1939b) states that Placopsis gelida is sorediate 

 in the eastern Spitsbergen islands. For our consideration this phenomenon 

 is of great importance since Placopsis gelida is often sterile and without 

 apothecia in the Arctic. Besides, reproduction by spores is relatively com- 

 plicated, more so than we used to imagine not long ago (cf. Ahmadjian, 1960), 

 and therefore not always effective in the Arctic. 



On the other hand, the antiquity of this species must be stressed. This age 

 derives from the fact that it is spread not only in the Northern Hemisphere, 

 but also in the southern one, with a great gap between its distribution in the 

 north Pacific and in the Southern Hemisphere. It is not unlikely, therefore, 

 that it could have survived the Last Glacial period even in more northern 

 localities than Lamb (loc. cit.) supposes. 



Soredia otherwise are found only in a few Arctic macrohchens, and if 



