72 ERIC HULTEN 



certainly old. That diverse types have developed to such a large extent indicates 

 that a very long time has been at their disposal. 



The plants which show the most obvious connections over the Atlantic are 

 those with a more or less Circumpolar area, at present having a northern 

 boundary line fairly far to the north. The distance between the American and 

 European continents is smallest in the north where the connection is strongest. 

 Plants like Poteiitil/a stipularis and Draba sibirica show that occasional 

 introductions are possible over long distances there. It seems probable that 

 the Circumpolar flora may have been spread by the wind blowing over the 

 frozen Polar Sea or by floating on ice. We know that nowadays on the large 

 floating Ice Islands in the Arctic Sea, Uving, well developed, flowering plants 

 occur, drifting around the Polar Basin. 



As the flora around the Polar Basin apparently is an old one only a few 

 introductions are necessary in every century to account for a fairly even 

 distribution. 



The strongest botanical argument for a land-bridge over the North Atlantic 

 is the Amphi- Atlantic plants although only little of the supposed connection 

 is to be seen today, even in this group. Many species are missing in Greenland, 

 on Iceland, and ,6n the other Atlantic islands. The present ranges, however, 

 could be interpreted as centering around the Atlantic, thus indicating that 

 they once spread from a center there. But they may also be explained as 

 reductions of former Circumpolar ranges caused by changing climatical 

 conditions. 



T^.endSmics occurring in the Atlantic sector are very weak indicators of a 

 vious connection. 



The phytogeographical conditions around the North Atlantic thus, give 

 poor support for a land-bridge that could have existed in Quaternary or Late 

 Tertiary times. 



