198 University of California Publications in Agricultural Sciences [Vol. 2 



found a female Drosophila melanogaster with five pairs of chromosomes 

 which originated after secondary non-disjunction in both parents. 



Assuming that Crepis tectorum, a species with four pairs of 

 chromosomes, originated by non-disjunction of one pair of the capil- 

 laris chromosomes, we would Expect a cross between these two to be 

 compatible inasmuch as the chromosome complex should be identical, 

 tectorum merely having one of the capillaris chromosomes in duplicate. 



The demonstrated inability of hybrids between the two species to 

 function normally leads to the conclusion that Crepis tectorum is not 

 related in such a direct way to Crepis capillaris. 



The results reported here indicate the desirability of making pre- 

 liminary experiments in hybridizing all the species of Crepis that give 

 promise of being of value for genetic investigations. Experiments 

 with other species are now under way. 



Grateful acknowledgment is made to Dr. Ruth F. Allen for her 

 assistance in preparing the cytological material. 



