230 KNUT F^GRI 



On the other hand, it must also be admitted that biologists should take up 

 the problems for some fresh thinking. Is centricity anything more than one 

 might expect from actual ecologic conditions? Nobody has tried to give an 

 objective answer to this, but it is a fact that very few, if any, other areas in 

 Scandinavia offer the same combination of favorable bed-rock, climate, and 

 topography. If this is enough to explain the distribution without recourse to 

 other factors, centricity loses much of its argumentative value. 



Some of the "rare" mountain plants possess good means of dispersal; 

 others seem to be in a rather unfavorable situation. The example of the Post- 

 glacial immigration of Phms and Corylus shows that our evaluation of dis- 

 persal potentialities does not always give the right result and should be an 

 admonition of some prudence. But it must be admitted that a species like 

 Stellaria crassipes certainly represents some problems, although an auxiliary 

 hypothesis of a Late Quaternary development towards reproductive sterility 

 is not in principle more — or less — improbable than the hypothesis of survival. 

 With its present degree of sterility it is even difficult to think how the species 

 could migrate from coastal refugia to its present stations. 



Another species that has presented some difficulties is Carex scirpoidea, 

 known in Europe from two stations at Solvaagtind only. The rest of its area is 

 American, and the species is the most extreme West-Arctic of all. Carex 

 scirpoidea is dioecious, and any attempt at explanation involving long- 

 distance dispersal would have to account for simultaneous dispersal of a 

 "male" and a "female" seed, which would seem rather unlikely. In itself 

 that may be used as an argument for rarity of the species in Europe. However, 

 a monoecious form, f. isogyna Dyring, has been described from Solvaagtind. 

 This suggests another solution of that particular problem: the Solvaagtind 

 occurrence may derive from accidental long-distance dispersal of a seed with 

 a "monoecious" tendency. Similarly, monoecious plants are found in at least 

 Greenland. 



Conditions in north Scandinavia are more complicated than in the south. 

 In the eastern part there is a separate flora element with Crepis multicauUs and 

 Oxytropis deflexa as its most famous representatives. The nearest stations are 

 far east in Asia, and none are known to occur in the intermediate mountains, 

 especially not in the Urals. I would consider it very possible that these species 

 have survived the last glaciation in or near Scandinavia, but can see no 

 reason compelhng us to reject the hypothesis that they survived at the edge of 

 the glaciated area in the U.S.S.R. The absence of these species there now is 

 easily explained by reference to their ecologic demands and the Post-Glacial 

 Hypsithermal period forests that would have crowded out these and many 

 other species from their former stations. As survival during a glaciation and 

 re-immigration must entail great losses, the absence of these species in the 

 Urals is not remarkable, although the Ice Age should have made itself less 

 felt in those eastern areas. 



