48 E. B. Babcoc\ 



If it be admitted that two such genetical processes as reduction 

 in chromosome number from 10 to 8, and interspecific hybridiza- 

 tion followed by amphidiploidy, may have occurred in the early 

 evolution of this group of plants, a working hypothesis of the 

 origin of the Crepidinae is readily forthcoming. This hypothesis 

 is illustrated diagrammatically in figure 12, and may be stated 

 as follows : 



(i) The original progenial stock consisted of one or more 10- 

 chromosome species. 



(2) New species with 8 chromosomes originated through some 

 such process as reciprocal translocation with subsequent elimina- 

 tion of parts of chromosomes, leading eventually to the disap- 

 pearance of one pair of chromosomes. 



(3) The genus Crepis arose from the complex of species thus 

 created. 



(4) The 8- and 9-paired species of closely related genera origi- 

 nated through interspecific hybridization between 5-paired and 

 4-paired species (or between 4-paired species) followed by am- 

 phidiploidy. 



(5) Speciation and evolution, within Crepis at least, have in- 

 volved the same fundamental processes together with autopoly- 

 ploidy, and, concurrendy with these processes, genie mutation 

 has played a continual role. 



The propositions just stated are submitted as the most logical 

 conception of the early course of evolution in the Crepidinae on 

 the basis of the evidence now available. Future research on 

 Crepis and especially on the genera closest to Crepis may result 

 in modification or extension of the hypothesis, but it appears 

 that the general nature of the processes involved in the evolution 

 of this group of plants has been disclosed. If this working hy- 

 pothesis ultimately becomes an established theory, it will necessi- 



