THE CONTINENTAL ELEMENT IN THE 

 FLORA OF SOUTH SWEDEN. 



Hv RIKARD STERNER. 



INTRODUCTION. 



The flora of tlie Middle European plain ^ (as will be shown in detail in the 

 course of this work) may with reason be regarded as being in a com- 

 paratively high degree homogeneous, if we consider the extent of the 

 region and the heterogeneous geographical conditions within it. Among the breaks 

 of uniformity that exist there should be noted the disappearance, towards the 

 west of Europe, of species that are found in the east. The western limits of 

 these continental species form a very pronounced characteristic of the flora of 

 the central and western parts of Middle Europe. 



An examination of the nature of these limits offers much that is of interest. 

 The question as to whether there are other causes of the distribution of species 

 than the existence of suitable localities becomes acute here in an interesting way. 

 On the one hand, these species, which are widely distributed in continental districts, 

 must have certain ecological features in keeping with the physical conditions in 

 those regions; and it seems probable that certain species at any rate have ecolo- 

 gical demands that would not have so many possibilities of satisfaction in maritime 

 districts. On the other hand, the history of the Middle European flora during 

 the Quarternary era tells us about various paths and dates of immigration and also 

 about strong dislocations in the distribution of species, brought about by great 

 changes in the climate and in the nature of the soil, which have been of specially 

 great importance to continental species. 



Much attention has been given to the western limits of continental species by 

 phytogeographers. They have especially played a conspicuous part in discussions 

 and examinations of the history of the Middle European flora. 



The present work may be looked upon as a contribution to the analysis of the 

 distribution of continental species in Western and Central Europe. 



^ Throughout the present work I have made use of a distinction between the terms ^Middle Europe" 

 and ^Central Europe* as follows: Middle Europe comprises the European Boreal forest-zone south of 

 the oak-limit; Central Europe comprises approximately the distribution area of Abies pectinata, the 

 south-eastern parts of it excluded; thus it comprises Central and Eastern France, Central and South 

 Germany, Switzerland, Austria, and Czechoslovakia. 



lO Geogfafiska. Annaler i<)22. 



