Chapter III 



-31- 



On Areas 



present data obtained by Samuelsson (1910) from a study of the areas 

 of several species endemic to the Scandinavian peninsula. His maps of 

 the distribution of Hieracitim meticeps and H. chloroleucum give a clear 

 picture of the character of the areas of these species and the centers of 

 greatest frequency of their stations. These centers of frequency are at 

 the same time the centers of origin of the areas of these species. 

 Samuelsson considers these species to be of comparatively recent 

 origin, having arisen during the Ice Age after the end of the last 

 (Mecklenburg) glaciation. Each arose— possibly by mutation— at a 

 certain point, which became the center of its area, whence dispersal 

 proceeded in various directions. The present boundaries of these areas, 

 therefore, cannot be regarded as climatic boundaries. They merely 

 mark in each case the limits of that territory which the given species 

 has succeeded in occupying at this stage of its dispersal, a territory 

 which in the future will continue to expand. 



With respect to the terminology of the concepts of the center of an 

 area, Arwidsson (1928) has proposed that those areas entirely in- 

 cluded within the limits of one well-defined region be called unicentric, 

 in contrast to bicentric (embracing two regions), tricentric, etc., or poly- 

 centric areas (Christ), if there are many such centers. 



As an example of how the center of maximum variation of a genus 

 may be located— without giving, however, any indication as to the 

 primary or secondary nature of this center — we may take the data of 

 Shirjaev (1932) on the area of distribution of the genus Ononis. The 

 species and subspecies of this genus are distributed throughout the 

 world as follows: 



From a study of these data Shirjaev draws the conclusion that the 

 center of origin and development of the area of the genus Ononis com- 



