352 



RIKARD STERNER 



of distribution are shared by Melampy- 

 rum nemorosum with other species. In 

 particular, its distribution exhibits several 

 points of agreement with that of Cynan- 

 chuvi vincetoxictini. 



I have submitted the distribution of 

 Cynanchum in the south of Sweden to 

 an extremely searching examination. But 

 as this examination is not yet completed, 

 only a brief report can be inserted 

 here. 



Cynanchum has an extensive distribu- 

 tion in Middle Europe (Plate i8). In 

 Russia it also occurs abundantly in the 

 steppe region. Nevertheless it does not 

 appear to belong to the true steppe, 

 but to the steppe-forest oases (»non est 

 planta vera stepposa», Korshinsky 1898, 

 p. 289). In Central Russia, as also in 

 Central Europe, it grows especially in 

 rocky escarpments and on rocky flat 

 ground. In the south of Sweden this is 

 the most usual way in which the species 

 occurs (see analyses in table 4, Ap- 

 pendix II). In the coastal skerries, and 

 in certain mainland districts lying only a very little above the sea, it may also 

 be met with in dry wooded slopes, especially on stony ground. 



As. compared with the distribution of Melampyrum, that of Cynanchum 

 differs by being quite continuous along the east coast, so far as the skerries 

 extend, and by the fact that the species is lacking in the interior of Blekinge 

 and in the south of Smaland. In the greater part of south-eastern Sweden, 

 however, the situation of its distribution limit up-country very largely coincides 

 with the limit of Melampyrum. 



In order to obtain, if pos.sible, some clear idea as to the causes of this distribu- 

 tion-limit up-country, I have first and foremost sought to determine the distribu- 

 tion in detail. 



As Cynanchum in the interior of the country occurs all but exclusively in 

 rocky escarpments or cliffs, it is only natural to seek a connection between the 

 distribution of the species and that of the localities mentioned. It appears that 

 the absence of the species in the south-west of Sodermanland has its principal 



Fig. 26. The distribution of Cynanchum vince- 



toxicum in Scandinavia and Finland. 



O ; uncertain occurrences, Cf. Plate l8. 



In Denmark the species has a few occurrences 



also on Fyen and is found in one locality in 



north-eastern Jutland. 



