72 EAST— STERILITY IN CERTAIN PLANTS. [April 23, 



(B) On the other hand the facts may be interpreted without 

 assuming irregularities of chromosome distribution if (i) there is 

 a group of chromosomes in each parent that cannot be replaced by 

 chromosomes from the other parent; if (2) there is a group of 

 chromosomes from each parent, a percentage of which may be re- 

 placed by chromosomes from the other parent, but where func- 

 tional perfection of the gametes varies as their constitution ap- 

 proaches that of the parental forms ; if (3) there are other chromo- 

 somes that have no effect on fertility and therefore can promote 

 recombinations of characters in the progeny of fertile F^ plants ; if 

 (4) a naked male nucleus entering the normal cytoplasm of the egg 

 in the immediate cross can cause changes in the cytoplasm that will 

 aft'ect future reduction divisions; if (5) this abnormally formed 

 cytoplasm is not equitably distributed in the dichotomies of gameto- 

 genesis in the F^ generation; if (6) it follows from (4) and (5) 

 that Fo zygotes may be formed which are less perfect in their 

 gamete forming mechanism than those of the F^ generation; and 

 if (7) the heterotypic division of gametogenesis does not necessarily 

 form two cells ahke in their viability. 



BussEY Institution, 



Harvard University. 



