THE CONTINENTAL FLORA OF SOUTH SWEDEN 353 



cause in the fact that suitable localities are rather lacking. To some extent the 

 same would seem to be the case also with the distribution in Uppland and Vast- 

 manland. However, for the first-named province, at least, there might hold good 

 the same connection between the distribution c)f this species and the geographical 

 development of the land that has been pointed out with regard to Melampyrum 

 nemorosum. In the districts where, owing to the influence of cultivation, forests 

 have never been able to occupy a land-surface, therefore, Cynanchum would seem 

 to have retained, to a very large extent, its skerry occurrences. It must also be 

 noticed that Cynanchum has its occurrences situated on such levels that they 

 must have come into existence during the Sub-boreal period, during which the 

 spreading of this xerothcrmous species must have been favoured (Cf. above 

 p. 316). 



In Ostergotland the distribution of Cynanchum shows no accordance with the 

 distribution of suitable localities. Further inland than the species reaches in that 

 province, especially near the lakes in the Stanga-valley, there is an abundance 

 of suitable escarpments, many of which nourish an unusually abundant flora. 



A close scrutiny of the distribution of Cynanchum in this last named district 

 is of great interest (See Plate 9). 



From its abundant distribution in the coastal district of Tjust (the northern 

 part of the Kalmar county), which the map shows in its entirety only for one 

 or two minor areas, Cynanchum has long rows of occurrences up into the 

 country. Here it follows the sharply-defined valleys which are characteristic of 

 that region. Along such a valley the species passes in one place even into 

 Ostergotland, passing the boundary in the parishes of Dalhem and Oppeby. In 

 the eastern part of the latter parish, on the shores of Lake Bjorken, there have 

 been at the disposal of the species excellent rocky escarpments in an unbroken 

 sequence into the lake-basins of the Stanga valley. In this, as has been men- 

 tioned, the species might have been expected to make its way in great abundance. 

 Nevertheless it is only to the eastern part of Lake Asunden that Cynanchum 

 has reached. In view of the fact that Cynanchum has an extremely good dispersal- 

 equipment — flattened, winged seed provided with a powerful pappus — it is 

 extremely curious that the species has not made its appearance in the numerous 

 other suitable localities. 



Other peculiarities in the general behaviour of the species in the south of 

 Sweden seem to me to show that dispersal by means of seed does not take 

 place to any great extent. 



In the first place I have never been able to find the species in suitable 

 localities more or less recently created by human intervention, such as rock- 

 blastings by the side of roads or railways, or dry, excavated, wooded hillsides; 

 and in the second place the exceptional position pointed out above on p. 340 



