THE CONTINENTAL FLORA OF SOUTH SWEDEN 253 



tlie semi-arid or seini-humid types of soil (Ramann 191 1, Wiegner 1918). The 

 black earth, »chernozyom», a soil with an enormous content of mould, is character- 

 istic of large parts of the Russian steppe. 



From the South-East European steppe region the continentality of the climate 

 decreases towards the north and the west. The precipitation increases, and also 

 becomes more even, as the ground becomes wooded. The summer temperature 

 decreases too, although it still reaches a considerable height in North-East Europe. 

 Geographical conditions of a more continental character occur only edaphically. 

 Because of the topograpJiy the precipitation and temperature conditions may 

 become abnormal within minor areas and deviate towards continentality. This 

 occasions more continental soil-types. Lime-districts likewise get a more or less 

 continental soil, especially in localities where the exposure is favourable. 



If we examine the isolated localities or minor distribution areas of the steppe- 

 species in Central and Western Europe, we shall easily be able to prove the 

 close connection between the edaphic development of the soil and the climate 

 towards continentality, on the one liand, and the distribution of steppe species 

 on the other. In the same way local conditions of climate and soil correspond 

 to the numerous isolated occurrences of a steppe flora far north in the East 

 European forest region. 



The north-easterly — south-westerly boundary that is characteristic of the distribu- 

 tion of many steppe species may be connected with the summer temperature, 

 which sinks from the east to the west, as also with the rainfall and cloudiness, 

 which decrease towards the south in Western Europe. 



Hence there would seem to be a coincidence between at any rate the general 

 features in the distribution of the steppe species and continental geographical 

 conditions in Europe. 



An important question to be answered is to what extent such a coincidence 

 also exists concerning the continentally distributed species that belong to other 

 distribution-types and other vegetation-tj'pes of a less conspicuously continental 

 character. 



It is a rather universal ecological feature in all the species here called conti- 

 nental, that, in their occurrence in nature, they have proved to be heliophilous. 

 This must be looked upon as a continental feature. Towards more maritime 

 regions, where the rainfall and the cloudiness are greater, and where the vegeta- 

 tion, in its quite natural state, would to a great part consist of close, umbrageous 

 forests, the species would naturally seem to have fewer possibilities of getting 

 their demand for light satisfied. We have seen that several of the rather few 

 continental species of the » grove » flora biologically occupy a separate position by 

 having their most important life functions fixed at a time when the supply of 

 light at their stations is at its greatest. 



18 



Geografiskn Annaler iq22. 



