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cases only one sex is heterozygous and the other is homozygous; 
and this is the conception now generally entertained by those who 
adopt a Mendelian explanation of sex. According to this view, if 
the male is heterozygous, as has just been decided to be the case in 
Lychnis, the female must be homozygous. As there are two kinds of 
homozygotes, namely, “positive” and “negative” (SHULL 9g), there 
remain two possibilities regarding the nature of the female; it 
may be either a positive homozygote or a negative homozygote. 
While either of these assumptions will explain about equally well the 
facts brought to light in Bryonia, neither will fit all those observed 
in Lychnis without encountering important difficulties. 
Making first the supposition that the female is a positive homo- 
zygote, as suggested by CasTLE (3), all conditions found in Bryonia 
will be satisfied if it be also assumed that B. alba is a homozygous 
monoecist (a modified female condition in this case) in which the 
absence of the monoecious character is dominant over its presence. 
The sterility of the F, hybrids in Bryonia unfortunately makes it 
impossible to test the correctness of these assumptions. It is less 
easy to make a positive homozygous condition of the female fit the 
results found in Lychnis as described in this paper. This can be 
done, however, by assuming: (a) that all egg cells of both females 
and hermaphrodites carry the gene for the female sex, and not 
that for hermaphroditism; and (b) that all the sperms of the her- 
maphrodites carry a gene for the hermaphrodite modification, regard- 
less whether they possess the gene for the female sex (the “¥ 
element”) or not. The first of these assumptions seems necessary 
from the fact that the results are identical in each case, whether 
a female or a hermaphrodite is used as the female parent; and — 
the second from the fact that females and hermaphrodites result 
from pollinating a normal female by pollen from a hermaphrodite. 
The second proposition might be replaced by one involving spurious 
allelomorphism. It is expected that a second generation will demon- — 
strate the correctness or incorrectness of these several hypotheses. 
The alternative assumption, namely, that the female is a negative 
homozygote, will just as simply represent the conditions of the F; 
generation. If the monoecious character in Bryonia be considered a 
modified male condition similar to the hermaphrodite character of 
