360 BOTANICAL GAZETTE [NOVEMBER 



uniform germ cells, and is to be considered homozygous, if the 

 other sex is demonstrated to have two types of germ cells. 6 



No chromosome differences have been found in Lychnis dioica 

 L. by STRASBURGER (36), who has studied a form of this species 

 known in German taxonomic works as Melandrium rubrum Gar eke. 

 His careful investigation of germ cells and root tips showed 24 

 chromosomes to be the somatic number, one pair of these chromo- 

 somes being notably larger than the rest, thus resembling the acces- 

 sory chromosomes or supposed sex chromosomes of the insects. 

 However, in Lychnis, the two members of this pair are indistinguish- 

 able from each other in both the male and the female. The same 

 results have been independently secured by Miss Luxz during the 

 past year, but have not yet been published. Lychnis appears to 

 agree, therefore, with Nezara, Oncopeltus, etc. (WJLSON 39, 40), 

 among the Hemiptera, as in these the two types of sperms, which 

 doubtless exist, are not visibly differentiated. STRASBURGER (36) 

 reports also that an investigation of Bryonia dioica has not revealed 

 the two types of sperms that might a priori have been expected. 



The hypothesis of unpaired determiners implies that a new 

 Mendelian character originates by the formation of a new gene 

 or the loss of an old one. My interpretation of hermaphroditism 

 in Lychnis dioica as due to an alteration in a sex gene already in 

 existence, which alteration does not in any way change the homology 

 of the gene in question, calls for a fundamentally different method 

 of origin of new characters from that involved in this extreme form 

 of the " presence and absence" hypothesis. The new genotype 

 which arises by mutation from the old one has in this case neither 

 more nor fewer genes than had the genotype from which it originated. 



The occurrence of male mutants among the offspring of my 

 genetic hermaphrodites appears to me to have a bearing upon this 

 question, as to the mode of origin of new characters. Among the 

 offspring of genetic hermaphrodites tabulated in this paper, n 

 male mutants appeared, and under case XII it is shown conclusively 

 that these are true males, and do not again give hermaphrodite 

 offspring, except probably in the extremely small proportion given 



6 As already noted, GUYER'S (14, 15) studies on spermatogenesis in the domestic 

 fowl and in the guinea fowl appear at present to be exceptions. 



