THE CONTINENTAL FLORA OF SOUTH SWEDEN 279 



judging the degree of probability of the occurrence of each separate species in 

 a certain district. 



Even if one or other statement should prove erroneous, nothing will probably 

 have to be abandoned in the conclusions and the discussions, as far as they are 

 based on floristic material. 



It would have been very desirable to publish the material in extenso here. 

 Space and expense have prevented this. The material is so extensive that this 

 treatise would be more than trebled in scope if the material were thus added. 

 All the statements have been accurately indexed, and a complete, suitably worded 

 list will be deposited and made accessible at some public institution. I further 

 hope to be able soon to publish at least the essential part of the material. 



TJie maps. 



The decidedly best way of making use of the material is to make it the base of 

 distribution maps. I have made such maps for a great number of the species 

 here treated. The method used is founded on the principle that the material 

 should appear directly on the map; the total dish'ibution of a s[)ecies will be 

 shown by the marking of the occurrences on the map. In analogy with what 

 has been the case in certain earlier phytogeographical works, of which that of 

 Andersson och Birger (1Q12) should be mentioned in the first place, I have 

 marked the occurrences with round dots of suitable size. With such a method 

 the distribution of species will appear in a completely exact and very clear 

 manner, as far as the material suffices. However, the application of this method 

 makes very great demands on the completeness of the material and hence ofi^ers 

 great difficulties. To prove the more or less common occurrence of a species 

 within a district solely by means of dots must meet with considerable difficulties, 

 as, naturally, statements of occurrence in such cases are only to be obtained in 

 a comparatively small degree. For the maps published in this work, however, 

 I have such a complete material that in the most cases a satisfactory view of 

 the distribution might be obtained through the distribution of the dots. 



The size of the dots has been determined b}' a compromise between the de- 

 mands that the map should be readily comprehensible and that it should be 

 accurate. If the dots are small, there must be dense occurrences to make the map 

 comprenhensible; if they are big, we shall miss valuable details in the distribution. 

 — A number of somewhat doubtful localities have been given on the maps and 

 indicated by rings. 



Three types of maps have been used. A more detailed one of South Sweden, 

 one of Scandinavia and one of Fennoscandia and Denmark. Besides, as has 



