E. V. Wulff 



-34- 



Historical Plant Geography 



Carex 



This table shows that, taking the greatest concentration of species 

 as a basis, Eastern Asia would appear to be the chief center of origin of 

 the genus Carex and the Atlantic Coast of North America the next 

 most important center. Judging by the concentration of each of the 

 three categories of species, the conclusion that these are the two most 

 important centers is confirmed, for they contain the greatest number of 

 endemic species. 



But in thus locating the center of an area it is necessary also to take 

 into account the fact, well known to every author of a botanical mono- 

 graph, that species themselves are not uniform, not of equal value. 

 This may usually be compensated for by the grouping together of 

 closely related species into sections, subgenera, and other such units. 

 Consequently, for the purpose of checking the conclusions as to the 

 center of the area of a genus arrived at on the basis of a calculation of 

 the number of species in the three categories, Szymkiewicz proposes 

 that analogous calculations be made of the number of sections or sub- 

 genera in each of the same three categories. Thus, one first calculates 

 the number of species of each of the three categories in each section, 

 and then, on this basis, determines the number of endemic sections, 

 sections distributed in two regions, and sections having a wide distri- 

 bution. As an example let us take the data obtained for the genus 

 Sisymbrium: — 



