Increase in Number of Species 



191 



Fig. 83. Distribution of the species comprising the genus Platijsamia. The 

 species kasloensis is considered to be of hybrid origin, having arisen from 

 eiiryalis and gloveri. (After Sweadner. ) 



Balkans to northern Greece, and A. cephalonica extends through 

 the mountains of central and southern Greece. Between these two 

 species and extending considerably eastward occurs a highly varia- 

 ble entity Abies borisii-regis which is in general intermediate be- 

 tween A. alba and A. cephalonica and which is considered to be 

 a hybrid species with A. alba and A. cephalonica as its parents 

 (Mattfeld, 1930; Stebbins, 1950). 

 In the Drosophila virilis complex the cytogenetics of the sub- 



