THE CONTINENTAL FLORA OF SOUTH SWEDEN 269 



With a few exceptions, the immigration of the South Swedish flora took place 

 from the districts south or east of the Baltic Sea. Can different routes of immi- 

 gration be iixed? And do they in any case determine the present distribution? 



In his important work y>Bidrag till den Skandinauiska Vegetatio7iens historian 

 F. W. C. Areschoug (1866) has called attention to the fact that among the South, 

 South-East or East European species in the South Swedish flora many are mis- 

 sing in Denmark, and a large number of them even in Skane, although localities 

 suitable for them can hardly be lacking in those regions. Following Forbes's 

 investigations into the history of the British flora and those of Sven Nilsson into 

 the history of the South Swedish fauna, Areschoug points out that this 

 fact would be fully explained if it could be proved that continuous land connec- 

 tions formerly existed between South-Eastern Sweden and the south or eastern 

 coast of the Baltic. In that case distinct routes of immigration would have ex- 

 isted to South-Eastern Sweden, thanks to which fact South-Western Scandinavia 

 {Skane and Denmark) may have failed to acquire certain of the species that 

 exclusively used those routes. — Areschoug also points out that some species 

 with a purely easterly distribution outside Scandinavia are to be found only in 

 Central Sweden and that they must have immigrated straight from the east and 

 cannot have been able to take possession of the whole of South Sweden. 



Grounds for the assumption of such land connections may be obtained in recent 

 quarternary geological investigations. Munthe points out that the height above the 

 sea-level of the southern shore of the Baltic formerly was much higher than now, 

 and he considers that, like Skane and the Danish Islands, Oland and Gotland had 

 next to land connections with the southern shore of the Baltic (Munthe »i9ioa», 

 p. 34; »i9iob»; cf., however, also Antevs 1922). These more or less hypothetical 

 land-bridges have been brought forward in the discussions of later times about 

 phytogeographical or zoogeographical problems (for instance, Schulz 1904 and 

 Hofsten 1919; from the latter work it is evident that there are rather strong 

 zoogeographical reasons for the acceptance of land-bridges). It would not seem 

 necessary, however, to demand any land-bridges in order to find the explanation 

 of the distribution of the plant-species mentioned. Attention should be paid to 

 the fact that the plants have a very important vehicle in the marine drift, Ser- 

 nander has shown the remarkable nature, quantitatively and qualitatively, of the 

 composition of the »Baltic drift* (Sernander 1894, p, iii; 1901 b, e. g. pp. 134 ff. 

 and 140 ff.). In any case we may safely leave it to the future to find out in wJiat 

 -manner this immigration may have taken place. 



Of greater importance from the present point of view it would be to find out 

 in what way the immigration routes of species may determine the present distri- 

 bution, and how far the distribution of species on the opposite side of the Baltic 

 coincides with a possible immigration from the east or south-east to South Sweden. 



19 Geo^ratiska Annalcr igsi. 



