358 - • RIKARDSTERNER 



We have thus before us a problem in plant geography which is of truely 

 considerable range, and assuredly we ought to ascribe to this problem a considerable 

 role in the floristic plant geography of South Sweden. In fact, we might reasonably 

 speak of a nCynaiichiiin problems in that region. 



The problem is, as will be seen, complicated, and probably its solution will 

 assume different shapes for different species. The only proper course of procedure 

 in this matter would seem to be to subject the distribution, biology, and ecology 

 of each separate species to careful examination. Until that has been achieved 

 the problem as a whole should be left open. 



Even now, however, it may be suitable to propose a working-hypothesis as 

 follows: Probably, there can be found a connection between the present distribu- 

 tion of certain species and the ])Ost-glacial upheaval of the land in the south- 

 east of Sweden, in the sense that species which in other respects have a distribu- 

 tion which is by no means tied to the shore of the sea, immigrated on to a former 

 coast and from there were able to extend only over the newly arising skerries, 

 but at the same time were able in certain cases to maintain some of their occur- 

 rences on the former shores. 



In order to throw still further light on this peculiar distribution, the following 

 points may be mentioned. 



One must not leave out of sight the fact that dim ato logical conditioiis may be 

 contributary causes with regard to certain species. The coasts of the south-east 

 of Sweden have a higher temperature in the late summer and autumn than their 

 hinterlands. In this connection, however, it must be noticed that the information 

 of the meteorological stations is not of much use as evidence when it is a 

 question of species whose ecology is in many respects dissimilar. The same 

 objection can be made against another climatological factor which in the case 

 before us may be regarded as important, namely the fact that the precipitation 

 greatly decreases towards the east in the coast districts. For such species as 

 Melica ciliata, Poa bulbosa, and Draba muralis these factors might well be thought 

 to be of importance. 



Sernander has repeatedly paid attention to the relation between the distribu- 

 tion of species and the post-glacial upheavel of land in South Sweden. Ahead}- 

 in his work of 1894 he has connected the distribution of certain species on 

 Gotland with the height above the sea-level of their occurrences and as has been 

 mentioned above on p. 316 he has in his paper of 190S from the same point of 

 view treated the history of the flora on the Upsala plain. 



Sundelin (19 17 and 19 19) has carried out comprehensive investigations into 

 the quarternary geology of the east of Ostergotland and Smaland. In so doing, 

 he has made interesting observations as to the fossil distribution of certain water- 

 plants. Trapa natans, Ceratophyllum demersum, and Najas flexilis had in former 



