26 



E. B. Babcoc\ 



to have certain chromosome numbers. From this representation 

 it is obvious that Eucrepis is much more variable in chromosome 

 numbers than the other subgenera. 



.\lthough 8 is the most prevalent diploid number in the genus, 

 10 must be considered more primitive, because the most primi- 



BARKHAUSIA 



45 SPECIES 



PEDITERRANEWM 



MOSTLY ANNUALS 



13 ENDEWIC OR LOCAL 



EUCREPIS 



120 SPECIES 



30 ANNUALS 90 PERENNIALS 



105 OLD WORLD 15 NO. AHER. 



40 ENDEMIC OR LOCAL 



CATOIMIA 



43 SPECIES 



OLD WORLD 



PERENNIALS 



20 ENDEMIC OR LOCAL 



Fig. 4. Phyledc relations of the subgenera of Crepis. 



tive species in the genus have lO chromosomes in their somatic 

 cells, and because no species having lo chromosomes are as 

 gready reduced or specialized as some of the species having 8. 

 It follows, therefore, that all the 8-chromosome species have been 

 derived from lo-chromosome progenitors; and similarly, the 

 two 6-chromosome species were probably derived from 8-chro- 

 mosome ancestors. The evolutionary processes involved in such 

 changes have been discussed elsewhere.** **" All numbers higher 

 than 10 are secondary, and have been derived by various pro- 

 cesses of which interspecific hybridization and doubling of the 

 whole chromosome complement are of most general importance. 



