280 RIKARD STERNER 



already been mentioned, attempts have been made to map the whole European 

 distribution of certain species. 



The occurrence material for the distribution of the species in Norway, Denmark 

 and Finland has for the most part been obtained from the literature. Regarding 

 Norway, the statements from the litterature have been supplemented by informa- 

 tion obtained from the collections of the Christiania and Bergen Museums, as well 

 as by unpublished observations by Mr. Ove Dahl, Conservator of the Museum, 

 and Mr. Rolf Nordhagen, Ph. D. Concerning a few »critical» species I have 

 myself gone through the collections which have kindly been lent to me. On 

 the whole, however, I have to thank Professor Jens Holmboe of Bergen and 

 Doctor Nordhagen of Christiania for these statements. — As to the distribution 

 in Finland, Professor Hj. Hjelt has shown me the kindness to let me make use 

 of the material of as yet unpublished parts of » Conspectus Florae Fennicae». Do- 

 cent W. Brenner, Helsingfors, has listed the localities of Ranunculus polyanthe- 

 mos in the herbarium of the Helsingfors Museum. Even on the South Swedish 

 maps occurrences in the neighbouring countries have been marked as far as the 

 map has allowed of this. Consequently it has been possible to include Aland, 

 regarding the flora of which a rich material of statements is accessible thanks 

 to Palmgren (19 15). The distribution there is of great importance to complete 

 the picture of the East Swedish archipelagic distribution. — Distribution-maps 

 have also been made for a few species that cannot be called continental accord- 

 ing to the previously laid down principles. It is important to know the distri- 

 bution of these species, as this in a high degree facilitates the comprehension of 

 the distribution of certain continental species. 



It is my hope that the distribution of the species will be adequately exhibited in 

 the distribution maps. A verbal account of the distribution of each separate 

 species, which would demand much space, will, I hope, be unnecessary. Con- 

 sequently the distribution of the species will be discussed below chiefly from 

 certain rather general points of view. These may be summed up thus: the ge- 

 neral distribution and mode of occurrence of the species in Europe will be exa- 

 mined; the distribution in South Sweden will be treated in relation to the mode 

 of occurrence of the species, to the geographical conditions (climate, soil condi- 

 tions, topography, influence of human intervention) and, as far as possible, to the 

 immigration history and biology of disseminating. An important object is to 

 arrive at some certainty with regard to the causes of the distribution limits. 

 Fixed results on this point can hardly be expected, because, as has already 

 several times been pointed out, our knowledge of the ecology and immigration 

 history of the species is much too scanty 



