334 



RIKARD STERNER 



the two distribution branches are marked also through the absence or very scanty- 

 distribution of the species in soiitliernmost Sweden (Skane): Seseli libanotis (Fig. 20) 

 is almost totally missing in southernmost Sweden, but it has many localities in 

 Southern Denmark, though it does not occur there further east than on the western 

 coast of Zealand. The case is similar, though less conspicuous, regarding Asperula 

 tinctoria (Plate 5), Potentilla arenaria (Plate 6), and Prunella grandiflora (Plate 6). 

 The two branches of distribution also mark two immigration routes to Scan- 

 dinavia, for usually the only localities suitable to the species were along these 



routes. Regarding the recently mentioned 

 species this immigration must have been 

 split up into two routes already before 

 the southwesternmost part of Sweden was 

 reached. This may have been the case 

 with the immigration of several other 

 species too, but as these are widely spread 

 in southernmost Sweden (Skane), the 

 original immigration routes cannot now^ 

 stand out distinctly. 



Hence in the distribution of the spe- 

 cies in question we should have examples 

 of the fact that the immigration route 

 determines the present distribution: in 

 Skane, which was situated off the immi^ 

 gration routes, the species did not spread 

 to any extent worth mentioning in spite 

 of the probable supply of suitable loca- 

 lities. In this connection it may be ob- 

 served that some steppe species, which 

 have only the westerly distribution branch, 

 are more or less spread in Denmark but 

 are absent in Skane, Trifolium alpestre 

 (Plate 6), Thesium ebracteatum, and 

 Eryngium campestre. 

 A number of species are lacking in Denmark but are spread in south-eastern 

 Sweden, and have consequently only availed themselves of the easterly immi- 

 gration route. Besides species with a more inconsiderable distribution in south- 

 eastern Sweden (for instance, Oxytropis pilosa, not to mention the species con- 

 fined to Oland and Gotland), Polygala comosa (p. 316) and Viola rupestris (p. 319), 

 should be pointed out. They have only a small number of occurrences in Skane 

 but are, especially, Viola, widely distributed in soiiiJi-eastern Sweden. Several 



Fig. 20. The distribution of Seseli libanotis in 



Scandinavia and Finland. 



O: uncertain occurrences. 



In Denmark the species has a number of occurrences 



also on Fyen, Lolland, and Samso, and in Schleswig. 



