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430 CECIL YAMPOLSKY 
sexes, and intersexes, as well as separate male and female plants, it is difficult 
to conceive of any exact quantitative separation of gametes such as is being 
postulated in animals. 
If there is segregation in the reduction division of sex determiners which 
are carried through the gametophytes, sex in the sporophyte would be 
determined at the fusion of the gametes, therefore syngamically determined. 
The work of Correns, which I shall later discuss, suggests, however, that 
sex may be determined before fertilization in the case of gynomonoecious 
forrrts when a form of more pronounced tendency comes together with one 
of a weaker tendency. 
Theories of Sex Inheritance and Sex Ratios 
It is the present tendency for investigators of animals and plants to 
assume that in dioecious species, whether of animals or plants, one or the 
other of the sexes is virtually a hybrid, that is, it is heterogametic. When 
the heterogametic individual mates with the homogametic individual, 
recessive for sex, there results a one-to-one ratio of sexefe. The dioecious 
organism is assumed to have either two kinds of eggs and one kind of sperm, 
or one kind of egg and two kinds of sperms. 
The behavior of the sex chromosomes in animals fits well with the 
contentions of the investigators who claim that sex is inherited in the 
ordinary Mendelian fashion. To be sure, the number of animal forms that 
have been shown to exhibit this quantitative difference in their sex cells is 
so far relatively small, yet an increasing number of forms is constantly 
being added to the list. 
The common observation that in dioecious forms there is approxi- 
mately a one-to-one ratio in the proportion of the sexes lends itself very 
readily to the analysis of sex on the basis of Mendelian formulae. The 
work of Morgan (1909) and von Baehr (1909) on phylloxerans and aphids, 
in which all the fertilized eggs produce females, because of the production 
of sperms from the spermatocytes of which only those with the X-element are 
functional, demonstrates in these cases a selective mortality of sperms 
(or spermatocytes) of one kind. Upon fertilization the homogametic 
eggs are fertilized by only one kind of sperm, and this explains the appear- 
ance of one kind of individual to the exclusion of the other. 
On these theories, sex is determined syngamically at the union of the 
two gametes. If the male is heterozygous for the sex factor, a female 
arises when the egg unites with a female-determining sperm, a male when 
the egg unites with a male-determining sperm . If the female is heterozygous 
for the sex factor, a female arises when a female-determining egg unites with 
any sperm, a male when a male-determining egg unites with any sperm. 
This syngamic determination of sex should exclude any" possibility of sex 
alteration prior to fertilization or after fertilization. It is to be noted that 
the sex chromosome theory does not attempt to explain how plants with 
