E. V. Wulff 



—182— 



Historical Plant Geography 



found themselves under particularly favorable circumstances as regards 

 protection from the decrease in temperature and humidity during the 

 Quaternary period. 



In all the rest of Europe and North America and also in northern 

 Asia we find a great impoverishment of the floras, increasing from 

 south to north, clearly testifying to the catastrophic changes which 

 their floras have undergone since the Tertiary period. 



From the foregoing it is quite clear that the origin of most genera 

 of angiosperms, including tropical genera, was in all probability linked 

 with those considerable territories embraced by the tropical and sub- 

 tropical zones. Thus, in Europe the location of these zones in Cre- 

 taceous and Tertiary times made possible the origin and development 

 of angiosperms throughout this entire continent, from its southernmost 

 boundaries to our present arctic regions. Then the subsequent shifting 

 of climatic zones, accompanied by changes in the habitat conditions of 



Fig. 28. — Same as in Fic. 25, but in the Miocene. (After Koppen and Wegener). 



the vegetation, resulted in their dying out over considerable territories 

 and in a shifting of the habitat regions. Consequently, our present-day 

 tropics and subtropics and those regions characterized by a Mediter- 

 ranean tj^e of flora constitute territories where there has been pre- 

 served Tertiary vegetation, which formerly had a different and a 

 considerably more extensive distribution. Hence there is no need to 

 assume that the angiosperms originated in the polar regions, as do the 

 advocates of the polar origin of floras, or that their origin was strictly 

 confined to the region of our present-day tropics. 



Phytogeographical Confirmation of the Theory of Continental Drift: 



— In the numerous phytogeographical papers published during the past 

 two decades there are many data confirming the basic principles of the 

 theory of continental drift. We can here present only a few of the 

 most important of these data. The most comprehensive investigations, 

 founded on an abundance of experimental data, aiming to test the 

 theory of continental drift on the basis of the geographical distribution 



