PARTHENOGENESIS 



181 



bring this case into line with the rest of our informa- 

 tion bearing on the relation of the chromosomes to sex. 

 One important point still remains to be explained. 

 What causes some of the migrants to produce large 



PHYLLOXERA CAKWECAUIJS 



7>lcct* 



9? tern, 7?lcthv& -C 



O 



o 



O 



9 f? 



O 



o 



o 



FIG. 93. Chromosomal cycle of P. carycecaulis. 



