IMMIGRATION AND DISPERSAL OF THE SCANDINAVIAN FLORA 229 



which must have immigrated across very great distances. True, tlie number of 

 species known from this flora is low, and they are well equipped for dispersal. 

 Nevertheless, their early appearance at Jaeren — isolated by ice and sea — 

 can hardly be explained unless iceberg transport from Denmark or some 

 other place is resorted to. Even today icefloes transport great quantities of 

 Danish rocks to the Oslo area. There is nothing inconceivable in iceberg (or 

 -floe) transport of diaspores as weU as of the flint and amber (Holmboe, 1912; 

 Johansen, 1957) found in west Norway. 



Whereas the possibility of immigration from Denmark has been recognized 

 for a long time, other possibilities have opened up later. The role played by 

 the North Sea continent is certainly very difficult to evaluate, but in Britain 

 more and more remains of an Arctic Ice Age flora are coming to hght. 



The recent finds in the British Isles of such exclusively Arctic species as 

 Koenigia, Artemisia norvegica, Diapensia lapponica, and others throw a new 

 and unexpected light on the problems of survival of our mountain flora. 

 Mention should also be made of the Scapiflora Papaver seeds found by 

 Conolly (1958) although the possibihty cannot be ruled out that they were not 

 identical with the Scandinavian Scapiflora. 



If Pleistocene Britain has been a refugium of our mountain flora it is no 

 wonder that we find no traces left of it there: in the humid climate of the 

 British Isles the ensuing humus cover must have been almost fatal for 

 the Post-Glacial survival of these plants as were the salt waters covering 

 the North Sea continent. It is remarkable that anything is left at all. 



The restriction of the Scandinavian mountain flora to the two well-known 

 centers represents a challenge. So does the apparent isolation of the West 

 Arctic species. A solution to the problem has been off'ered by biologists : the 

 hypothesis of Ice Age survival within Scandinavia. Incidentally, if survival is 

 accepted for the Last Quaternary Glaciation, it is very difficult to get away 

 from the same argument for earlier ones. 



The idea of Pleistocene survival, so brilliantly presented and defended by 

 Nordhagen (1933) has met with very strong, almost passionate resistance from 

 geologists. Each argument has been met with a counter-argument, and for 

 many years now httle new has been presented : the protagonists of the two 

 opinions have mostly been riding their rather age-worn hobby-horses. 



It is easy to see that some of the consequences drawn from the Ice Age 

 refugium hypothesis are incongruous, like Lindroth's (1949, p. 775) series of 

 refugia in places where we know positively that there cannot have been any, 

 or Lindquist's (1948) idea of the survival of Picea abies (cf. F^egri, 1950). 

 However, it does not disprove a theory that erroneous conclusions have been 

 drawn from it. 



It should also be said that geologists have been completely negative in their 

 argumentation: the two main problems of centricity and West-Arctic distribu- 

 tion exist, and they demand an explanation. 

 Q 



