HISTORY AND AGH OF SOME ARCTIC PLANT SPECIES 209 



ca. 7,000,000-10,000,000 years, this period was certainly sufficient for the 

 formation of the bulk of the Eoarctic flora from the Temperate or Sub- Arctic 

 flora growing there in the Tertiary. 



But previously to this, a very similar flora was formed in the high mountains 

 of Eurasia and America. This flora was isolated for a long time and could 

 develop well-characterized taxa of even higher ranks than species. At the 

 end of the Tertiary new possibihties arose for such floras — the Arctic vegeta- 

 tion reached as far as some mountain ridges and the mountain flora of North 

 America and northeastern Asia could migrate into the Arctic and vice 

 versa-Arctic elements could penetrate into the interior of the continents or 

 far to the south. 



In the beginning the conditions were somewhat different in Europe itself. 

 Although certainly the Alps, the Pyrenees, the Caucasus, etc., had their own 

 mountain floras, they had no connection with the Arctic at first. Even during 

 the first Ice Age the contact between the Arctic and the Alpine floras was 

 probably minimal. The Arctic flora existed mainly north of the continental 

 ice-shield. Now the migration of plants occurs differently if these have to 

 penetrate into regions already occupied by other plants or if they have to 

 colonize land laid bare by sea or ice regression. We must therefore suppose that 

 the penetration of the Arctic element southwards was much slower, more diffi- 

 cult and less effective than the advance of the mountain flora northwards. The 

 First Ice Age could therefore hardly bring any Arctic elements to central 

 Europe and the central European mountain flora could scarcely give more 

 than a small contribution to the Arctic flora because the ice shield did not 

 reach so far south at that time (Fig. 2). 



Only during the Mindel and Riss Glacials, and partly also during the WUrm 

 period, could a greater exchange of plant species take place between the 

 central European mountains and the Arctic as well as between the Alpine and 

 Siberian elements. 



The exchange of the flora of the Arctic and of the mountains of America 

 and Eurasia was only partial; we know well enough that only certain mountain 

 species migrated to the north and that not aU Arctic species migrated to the 

 south although chmatic conditions seemed favorable to both. We must take 

 into consideration the ability of the mountain plants to five in the tundra 

 communities; there are sharp differences in the life conditions of the steep 

 mountain slopes and ridges and the mostly flat tundra. The capacity of seed 

 transport was also of some importance. These two factors combined brought 

 about a situation where certainly old oreophytic species of the European 

 mountains, as, for example, Carex firma (forming extensive and very charac- 

 teristic plant communities in the Alps, the Pyrenees, the Carpathians, and 

 the Karavanken, and elsewhere) did not reach north of the Tatra Mountains, 

 whereas Salix herbacea and other similar species migrated towards the north. 



It seems that there must also have been other factors influencing this 



