INHERITANCE OF SEX AND RELATED PHENOMENA 213 
4. Bryonia alba self-pollinated gives only monoecious plants. 
If we assume that all the pollen grains and ovules of Bryonia alba 
are of one kind which is indicated by the fact that it breeds true to the 
moneecious condition, then there is no escape from the conclusion that 
female plants of Bryonia dioica produce only one type of ovule but male 
plants produce two types of pollen grains. Unfortunately as is often 
the case in interspecific hybrids, the F, of this cross is sterile and con- 
sequently the analysis cannot be carried further. 
Shull, however, has studied the inheritance of sex in Lychnis dioica 
which is normally dicecious but occasionally produces hermaphroditic 
plants. Although this case has not yet been fully analyzed, the results 
thus far indicate clearly that the male is heterozygous with respect to a 
sex-determiner, and the female homozygous. The results of Shull’s 
investigations may be stated under several definite heads as follows: 
1. Females with pollen from males give substantially equal numbers 
of male and female offspring. 
2. Females with pollen from genetic hermaphrodites give equal 
numbers of hermaphrodite and female offspring. 
3. Females with pollen from somatic hermaphrodites give equal 
numbers of male and female offspring. 
4. Genetic hermaphrodites selfed give equal numbers of hermaph- 
rodite and female offspring. 
5. Genetic hermaphrodites with’ males give equal numbers of male 
and female offspring. . 
6. Females from whatever source are genetically identical. Thus 
females from the cross female hermaphrodite transmit the same sex- 
determiners as females from the cross female X male. 
7. In crosses between female and hermaphrodite a small percentage 
of mutant males always appears and in crosses between female and 
maleapproximately thesame percentage of mutant hermaphroditesappears. 
In the above résumé of the experimental evidence on sex-determina- 
tion in Lychnis, the equality of sexes was only approximate, in fact females 
usually occurred in excess, and sometimes in considerable excess. 
Shull has interpreted this evidence to indicate that in Lychnis the 
hermaphroditic condition results from a modification of the male con- 
dition, and that this modification is reversible as shown by the evidence 
in7, above. Interpreted in terms of the XY type of sex-inheritance then, 
females are XX; males, XY; and hermaphrodites, XY’; and the change 
from Y to Y’ is reversible. Clearly the results indicate that males and 
hermaphrodites are heterozygous with respect to the sex-determiner, 
and females homozygous, although later investigations which have not 
yet been fully interpreted indicate that some disturbing factors are at 
work, at least in certain cases. 
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