CASTLE: THE HEREDITY OF SEX. 207 
dominates in all unions with a crepuscularia (C) or a delamerensis (D) 
gamete. Tutt states that the species bistorta ‘ predominates” in crosses 
with crepuscularia. It would not be surprising, accordingly, to find 
that the sex-character borne by the ‘‘ predominant” gamete likewise 
dominates in the zygote. (2) Of the four possible combinations of 
gametes, one is sterile; namely, the combination, ovum B Q + sperm C 
(or D) g. The three fertile combinations are, — 
ovum B @ + sperm C (or D) 9, 
EOF C) COrGD Oeste, 
66 4 3b + 6“ B Q. 
A sufficient justification of this hypothesis is that it explains satisfac- 
torily the results observed. Those results are, indeed, peculiar, but 
there is no reason to question their accuracy, for they represent the com- 
bined and harmonious observations of two independent and competent 
experimenters. Calculating the sex-proportion in the various crosses on 
the basis of the two hypotheses stated, we obtain the results shown in 
Table II. For convenience in comparison, the observed ratios are placed 
opposite the calculated ones. 
TABLE II. 
Sea-proportions among hybrid offspring of Tephrosia. (Compare Table I.) 
Cross Calculated Observed 
(Table I.) Ratio. Ratio. 
[1] + [2] 
[3] + [4] 
The calculation has been made on the basis of a normal equality 
between the sexes. Asa matter of fact, males are normally slightly in 
excess of females, so that it is not surprising to find the calculated num- 
ber of males a little too low in nearly all cases. Not improbably the 
normal excess of males results from greater mortality among female 
larvee ; and since the mortality is especially high among hybrid broods, 
