SPECIES CROSSING 



195 



ing 24 or 25 chromosomes. There seems to be a chance 

 here of producing new stable types with a new chromo- 

 some number that may contain one or more pairs of chro- 

 mosomes derived from the species contributing the 



«&• 



setose 



Crepis 



biennis 





-> 





Fig. 109. 

 Chromosome groups of Crepis setosa and C. biennis. (After Collins 



and Mann.) 



smaller number. The presence of 10 conjugants in the 

 hybrid suggests that Crepis biennis is a polyploid, pos- 

 sibly an octoploid. In the hybrid the like chromosomes 

 unite in pairs. This F x hybrid, with half the full number 

 of biennis chromosomes, is an annual, while biennis itself 

 is biennial. The reduction in the number of its chromo- 

 somes has caused a change in its habits. It reaches matu- 

 rity in half the time necessary for biennis. 



