5© E. B. Babcocl^ 



that, in the mind of the present writer, all such queries revolve 

 around problems which are of minor importance as compared 

 with the genetic evolutionary processes on which the hypothesis 

 is based. One such question may be mentioned briefly by way 

 of illustration. 



An interesting issue is raised because, in those few species in 

 the genera related to Crepis on which data are available, there 

 appears to be only one pair of satellite-bearing chromosomes. 

 This may at first appear inconsistent with the fact that certain 

 species of Crepis are believed to have arisen through interspecific 

 hybridization and amphidiploidy because they have two or more 

 pairs of unlike D chromosomes. This criticism can be met by 

 reference to the phenomenon known as amphiplasty.^" It has 

 been found that, in hybrids between certain species, the satellite 

 contributed by one of the parental species is permanendy lost, 

 whereas in other interspecific hybrids the satellites from both 

 parents are preserved. These well-established facts are sufficient 

 to account for the apparent inconsistency. 



The genus Crepis is closely related to the other genera of the 

 Crepidinae, if the evidence from comparative morphology can 

 be trusted, and probably it can be, especially when it leads to the 

 same conclusion as other criteria. The genus Crepis, in spite of 

 the great variability in chromosome numbers which it exhibits, 

 is a natural group with a common center of origin and a single, 

 most primitive chromosome number. The center of origin of 

 Crepis coincides with the center of origin for its closest allies. 

 Only on cytological grounds is there an apparent separation of 

 Crepis from other genera in this group. A hypothesis has been 

 proposed which seems to account satisfactorily for these chro- 

 mosome relations and to be consistent with other evidence of 

 natural relationship in the Crepidinae. 



