330 R IK ARD STERNER 



Concerning this question we must admit the difficulty of explaining why the 

 species should have become extinct in these Central European occurrences. The 

 occurrence of the species on Oland should perhaps rather be taken as a result 

 of a long-distance dispersal through birds. 



From South-Eastern Europe there are migratory bird-routes to the Southern 

 Baltic (Palmen 1876; Duncker 1905; Lucanus 1922). For certain gull species, 

 especially Larus ridibundus, which breeds in great numbers in swamps on the 

 Alvar of Oland, there are migratory routes from the Hungarian plain to the 

 Southern Baltic (see, for instance, Lucanus 1. c, pp. 31 ff.). The birds would 

 generally seem to make the passage from South-Eastern Europe to the Southern 

 Baltic in a very short time (one day or so) without any pause. It seems to me 

 quite conceivable that the birds then, occasionally, bring with them such little 

 seeds as are here spoken of. As Plantago tenuiflora grows in Hungary in places 

 that are damp in spring, the edges of small bodies of water, lakes etc., (Kerner, 

 Osterreich. botan. Zeitschr. 1875, Prodan 19 15 and 19 16), where also many 

 migratory birds have their whereabouts, I consider it by no means unlikely that 

 the immigration of the species to Oland has taken place in this way. 



A similar explanation seems to me to be most likely regarding the former occur- 

 rence of Bassia hirsuta on Oland (at Ottenby). Its immigration would, however, 

 seem to have taken another route than that of Plantago. The species has a fairly 

 considerable number of occurrences in Southern Denmark and on the German 

 and Dutch coasts of the North Sea. Outside South Russia it occurs, besides, in 

 a few places in the Mediterranean region, inter alia on the French coast of the 

 Mediterranean (Plate 13). 



An important migratory bird-route runs from the south of the North Sea 

 across the Southern Baltic, where it turns off to the northeast or the north at 

 the southern end of Oland. Enormous masses of birds pause on or at the 

 southern end of Oland. Bassia might be supposed to have reached its locality 

 on Oland from the occurrences on shores of the North Sea through these birds. 



The birds get to the south of the North Sea across the Western Mediterra- 

 nean, the French Mediterranean district and the valleys of the Rhone and the 

 Rhine, and on the French coast of the Mediterranean Bassia has, as has been 

 mentioned, one of its Mediterranean areas of occurrence. 



In this connection attention should once more be paid to the peculiar distri- 

 bution area of Silene viscosa along the south-eastern coasts of Sweden and the 

 southern coasts of Finland, where very important migratory bird-routes pass along 

 (P- 325)- In this case also an immigration through birds from the Hungarian 

 plain or the South Russian steppes seems to me to be conceivable. 



To give any very great value to these hypotheses of dispersal by migratory 

 birds, of course, more evidence than has here been produced is wanted. Among 



