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dividual should likewise be a male, 

 since the ratios among the sex-deter- 

 mining genes are not different in the 

 two cases. 



Schrader and Sturtevant have at- 

 tempted a reconciliation of the cases 

 of Drosophila and the bee by use of 

 Goldschmidt's algebraic formulation. 

 They assign a positive value, e.g., +2, 

 to each A and a negative value e.g., 

 — 6, to each X. It is then assumed that 

 the effective relation is the algebraic 

 sum of the values of X and A, as given 

 in the column to the right in Table I. 

 On this view the haploid might be a 

 male. But this system has a difficulty 

 in that the intervals between successive 

 indices do not correspond very well 

 with the observed differences between 

 the sex grades. Thus the smallest ob- 

 served interval in fact, that between 

 the 3N and 2N individuals, is repre- 

 sented by a difference of 4 units, while 

 the very great interval between the 

 male and the female is represented by 

 only six units. At that time the 4N type 

 was not known; and when it is added 

 to the series, the fit is very poor on 

 the algebraic system and very good on 

 the ratio system. I repeat that I do not 

 regard the case of the bee as interpret- 

 able on the same basis as Drosophila 

 so long as the present account of the 

 mechanism for the bee is unchallenged. 



BRIDGES 



At present the difference between 

 haploid and diploid sexes must be 

 referred to the same type of deter- 

 mination as that responsible for the 

 larger size, rougher texture of eyes 

 and other slight changes that distin- 

 guish the 3N from the 2N individual. 

 But outside of the cases like that of 

 the bee, it seems probable that the 

 ratio type of interaction is the general 

 mode. In evidence of this may be cited 

 the vast array of monoecious plants in 

 which the sex relations in the triploid 

 and tetraploid remain the same as in 

 the diploid. Of course there is high 

 sterility in the triploid forms on ac- 

 count of the instability of the 3N 

 group in meiosis, and the consequent 

 production of inviable gametes or 

 zygotes. Among the most striking con- 

 firmations of this ratio view of genie 

 balance is seen in the mosses, through 

 the brilliant work of the Marchals, 

 Schweitzer and von Wettstein. For ex- 

 ample, they find in a moss with sepa- 

 rate sexes that a 2N gametophyte that 

 combines 2 female groups of chromo- 

 somes is a pure female, like the haploid 

 female plant (Table II). Likewise the 

 2N gametophyte that combines two 

 male groups of chromosomes is a pure 

 male plant, like the haploid male plant. 

 But a 2N gametophyte that combines 

 a male and a female group is no longer 



