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 



*>\^ 



seloss. 



Crepis 



-> 





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 Fj 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. 



