Chapter III 



—27— 



On Areas 



these species to different soils, such "adaptation" being determined by 

 competition between the two species. 



Center of an Area: — Of vital importance for the study and under- 

 standing of an area is the determination of that initial territory whence 

 a genus or species began its dispersal whereby it reached the present 

 boundaries of its area. This initial territory where an area originated 

 is known as the center of the area. One of the first definitions of the 

 concept of the center of an area was given by Robert Brown (1869), 



haufiges VorKommen 

 vereinz&It + ausgesforben 

 EniwoTfen vonHrBeger' 



Fig. 2. — Example of a discontinuous area. Localities of Euphorbia palustris, re- 

 stricted to the river basins of central Europe. (After Hegi). 



who formulated it approximately as follows: Each genus seems to have 

 arisen in that center in which the greater number of its species is 

 found; these centers have doubtless undergone many modifications 

 as a result of geological changes, and many anomalies in the distribu- 

 tion of plants may be thus explained. 



There are no grounds for presuming that a new species will not 

 extend its area beyond the limits of the region of its origin. It will, 

 without any doubt, begin to spread in all directions open to it, and the 

 region of its origin will constitute the center of the area being formed. 

 Further on we shall discuss more in detail the origin of an area, and we 



