THE CONTINENTAL ELORA OF SOUTH SWEDEN 351 



study the distribution in great detail (Plate 8). Over and above a very abundant 

 distribution in the skerries and on the coast, the species has a large number of 

 occurrences in the south-eastern portion of the province. In most cases these 

 occurrences are found on shores. In certain districts, especially round Upsala, 

 the species appears on slopes occupying the border zone between moraine hillocks 

 and the cultivated clay-fields lying at their foot. In connection with what has been 

 said above (p. 317) as to the abundant distribution of certain steppe species on 

 the Upsala plain, the explanation of this state of things would seem to be 

 found in the fact that wood-edges have existed here ever since the land came 

 into existence. At the time when the moraine hillocks formed islets and skerries 

 in a coastal archipelago, Melampyrum grew in wood edges on the shores; and 

 even after a continuous land surface emerged, the species has been able to retain 

 these occurrences owing to the fact that the clay areas have never been occupied 

 by forests in consequence of the intervention of man. 



West of the Upsala plain, Melampyrum has a smaller and somewhat isolated 

 distribution area, which falls within the above-mentioned (p. 341) moraine and 

 marsh ground region in the parishes of Jumkil, Jarlasa, Skogs-Tibble etc. In 

 these parts we can still study the mode in which the species naturally occurs: 

 it occurs abundantly in Calamagrostis-forests on the banks of (former) marshes 

 or lakes (see the analyses of vegetation in table 5, Appendix II). — The cause of 

 the gap in the distribution between this region of occurrence and the occurrences 

 down on the shores of Lake Malar to the south and on the plain of Upsala to the 

 east would seem partly to be found in the rarity of lakes and marshlands in the 

 intermediate region. [Another cause is perhaps to be found in the fact that this 

 region lies higher than the plain of Upsala and that its coming into existence 

 in the form of a continuous land-surface happened at a time when the popula- 

 tion of Upplaiid was still mainly engaged in fishing and had no reason for 

 preventing the forest from overrunning the entire surface of the land (Cf. Hbgbom 

 1912; Eriksson 1913; and Ekholm 19 15). Space does not permit of a more detailed 

 treatment of the interesting connection, here only hinted at, between the present 

 distribution of species in Uppland and the geographical development of the 

 land. J 



The distribution of Melampyrum nemorosum in Sweden, therefore, is in man\- 

 respects peculiar and is widely different from that of the species previously 

 treated. It would be particularly interesting to attempt to determine the causes 

 why the area of distribution is restricted to coastal districts. Why has not this 

 species, like the species with which it most abundantly occurs in its localities on 

 the east coast, been able to spread itself further over the country? 



The distribution of Cynanchum vincetoxiaun in the south of Sweden. t>The Cy- 

 nanchu))i probleni-A. Several of the above-mentioned peculiarities in the matter 



