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) 0/ the four possible combinations of 

 gametes, one is sterile ; namely, the combination, ovum B 9 + sperm C 

 (or D) ^. The three fertile combinations are, — 



ovum B S + sperm C (or D) 9, 



" C (or D) 9 + " B i, 

 " " <? + " B 9. 



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. 

 Sex-'proportions among hybrid offspring of Tephrosia. {Compare Tabic I.) 



The calculation has been made on the basis of a normal equality 

 between the sexes. As a 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 

 larvae; and since the mortality is especially high among hybrid broods. 



