PLANT MIGRATIONS ACROSS THE NORTH ATLANTIC OCEAN 

 Table 5 



185 



Number of Bivalents in Intraracial and Interracial Crosses in Papaver Lapponicum 



(based on Knaben, 1959). 



The mean number of bivalents with standard error of the mean given together with number 

 of PMC's counted and number of crosses. 



important point is that the genetic differences between ssp. scandinavicum 

 and the American ssp. occidentale and labradoricum is about the same as the 

 genetic difference between ssp. occidentale and ssp. labradoricum themselves. 

 \^ Papaver lapponicum once dispersed in both directions from the Pacific area, 

 the isolation between ssp. occidentale and labradoricum must be of a younger 

 date than the isolation between these two subspecies and ssp. scandinavicum. 

 This is not borne out by the observations made. 



As pointed out above, there is a fairly gradual transition in the flora from 

 Scandinavia across Scotland to Iceland and Greenland, and this applies also 

 to the fauna. This general feature can hardly be explained by the hypothesis 

 that the plants came from the Pacific area. The strength of the hypothesis is 

 that it avoids creating a new land-bridge, but in order to explain, for instance, 

 the European element in the flora of Iceland, it seems necessary to postulate 

 some land connection across the longest stretch of water now separating 

 America and Europe. 



THE HYPOTHESIS OF A LAND CONNECTION BETWEEN 

 EUROPE AND AMERICA 



By process of elimination, the conclusion is reached that the only hypothesis 

 capable of explaining the Amphi-Atlantic biota is that of a former land con- 

 nection across the North Atlantic Ocean. Since there is evidence that long- 

 distance dispersal has been of importance in the immigration of the western 



