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.° 
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 Garcke. 
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 Lutz during the 
past year, but have not yet been published. Lychnis appears to 
agree, therefore, with Nezara, Oncopeltus, etc. (WILSON 39) 4°); 
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, 1 
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 
‘As already noted, GuveEr’s (14, 15) studies on spermatogenesis in the domestic 
fowl and in the guinea fowl appear at present to be exceptions. 
