E. V. Wulff —156— Historical Plant Geography 



centers of dispersal. As such centers there must have served, first of 

 all, those territories and mountain peaks (so-called "nunataks") which, 

 although lying within the glaciated areas, were not covered by the ice. 

 That pre -glacial vegetation did survive in such places ijiay now be 

 considered a definitely established fact. 



Secondly, as centers of dispersal there served those territories lying 

 directly south of the ice-sheet's fringe. We now regard as erroneous 

 the opinion formerly held that during the Ice Age the vegetation was 

 destroyed not only on the glaciated territory but also in a wide radius 

 about it. There are data establishing the fact that the arctic (Dryas) 

 flora occupied only a more or less narrow strip along the edge of the 

 ice-sheet, beyond which the vegetation comprised herbaceous and 

 forest species of a more heat-loving type. This is evidenced by the 

 fossil tree-trunks and other parts of woody plants found within the 

 limits of this zone. Formerly, often solely on the basis of the fallaci- 

 ous assumption that at such a distance from the ice-sheet there could 

 have existed only tundra vegetation, such fossil remains were referred 

 only to the interglacial epochs. 



Thirdly, as centers of dispersal for the re-stocking of the territories 

 freed from the ice, there served those refuges or sheltered stations, pri- 

 marily mountain systems, where the Ice Age did not have such 

 catastrophic consequences for plant life and where there survived a 

 Tertiary flora, though in some cases in an impoverished state. 



There is a great diversity of opinion as to which regions retained 

 during the Ice Age their forest vegetation. The chief, and generally 

 recognized, refuges in Europe may be regarded as the following (from 

 west to east): the Mediterranean Basin, including the Pyrenees, 

 Cevennes, and other mountains of southern France, the Apennines, the 

 southern spurs of the Alps, and the mountain sj'stems of the Balkans; 

 the mountains of southern Germany (possibly also the Schwabische 

 Jura); the mountains of Lower Austria (possibly including the ad- 

 joining Bohmisch-Mahrische Hohen); the Carpathians and the Banat 

 hills; the mountains of the Crimea and the Caucasus and the adjoining 

 mountain systems of Asia Minor and Iran (Lammermayr, 1923). Most 

 of these mountain systems run east and west, in consequence of which 

 they constituted a barrier beyond which the heat-loving Tertiary vege- 

 tation could not retreat as it fled from the cold advancing from the 

 north. 



The impoverishment of the Tertiary vegetation was a slow process. 

 After each advance of the ice-sheet it lost a number of its elements. 

 Only the southern part of North America and those southern regions 

 of Europe protected on the north by mountain chains, such as the 

 Mediterranean Basin, Transcaucasia, and southern Crimea, retained a 

 large number of species of their pre-glacial flora. Consequently, the 

 vegetation occupying the territory freed from the glaciers was con- 

 siderably poorer than that inhabiting the same territory in pre-glacial 

 times. In North America, where the mountain chains run north and 

 south, the vegetation that retreated during the Ice Age did not en- 

 counter any such barriers as in Europe, and so it was able to migrate 

 considerably farther south. This explains why there is a greater per- 

 centage of Tertiary elements in the present-day floras of formerly 



