362 RIKARD STERNER 



cause of the incapacity of Cynanchum to spread further inland is to be sought 

 in its apparently extremely defective formation of fruit, which may have its cause 

 in the pollination biology of the species and the windy character of the rock cliffs. 

 The inland distribution limit of Cynanchum and, although not quite so clearly, 

 Melampyrum nemorosum coincides fairly well with the position of the coast-line 

 at the maximum extension of the Ancylus Lake. In that case, therefore, the 

 species would have their first distribution on the coast of south-eastern Sweden 

 at the time of that maximum extension. 



Chapter XI. 

 The other continental species in the flora of South Sweden. 



The remaining continental species belong to types of vegetation which are of 

 a less strikingly continental character. Their distribution conditions are, accord- 

 ingly, unlike those of the species previously treated in several respects and do 

 not offer the same interest as they do from our present point of view. 



For this reason, and also because of the very restricted space at my disposal, 

 these species will be treated with the utmost brevity. 



With regard to those species that may reasonably be assumed to be /ess bound 

 by climatological and soil conditions of a character other than those which are 

 found in the south of Sweden, it is of special interest to investigate to what 

 extent they have distribution limits and to what extent those limits differ from 

 those of the steppe and wooded hillside species, and what may be the causes of 

 those differences. 



Species of the Flood Meadows. 



In the immense forest areas of middle and northern Russia the vegetation 

 presents excessively little variety. What to some extent breaks the great mo- 

 notony of the forests and marshes is the vegetation of the river banks. Where 

 the rivers have cut their way downwards, and steep or sloping banks with a 

 suitable exposure have come into existence, there are possibilities for xerother- 

 mous species to exist; but where, on the other hand, the bed of the river is 

 wide and the banks are flat, there have been formed — at least in part with 

 the help of man — flood meadows having their own flora, which is especially 

 rich in herbs. 



