402 ^^ ■ Bateson. 



D R ? X D R CÎ gives DDcî DRd DR? RR? 

 RRÇXDRcî „ DRdRRcîDRÇRR? 



DRÇXRRc? „ DR^ RR? 



R R ? :< R R c? „ . . . . R R ^ . . . . R R ? 



Castle and Do ne a s ter sugg-est that all zygotes are hetero- 

 zygous in respect of sex-deterrainants, and that with these other 

 characters may be gameticallj^ coupled. In this particular case if 

 among the eggs of the heterozygotes all which bear S carry D, and 

 all which bear ? carry R; and if in the spermatozoa there is no 

 coupling, so that there are spermatozoa of all four combinations the 

 observed result will be produced. It is further assumed that that 

 sex is dominant which is borne by the egg. Doncaster is careful 

 to remark that this is not the only possible system which describes 

 the facts, but the case is of extraordinary interest as showing that 

 the facts of sex-distribution have a close connection with gametic 

 differentiation and may even be expressed in terms of a not impossible 

 Mendelian formula, though the formula cannot j^et be declared to be 

 in its final shape. In order to complete the experiment the cross 

 grossidariata ? X JacHcolor S has still to be made, and the result maj^ 

 not be unimportant. 



Unfortunately the direct experiments on the transmission of sex 

 have not yet led to a clear result. ( " o r r e n s (35) found in Satureia 

 and Silène that crosses between hermaphrodites and females gave 

 almost exclusively females and a continuation of the experiments is 

 ])romised.^) 



Other experiments of the same kind have come to an end through 

 the sterility of the cross-breds. For example the same writer dis- 

 covered (35) that the monoecious Bryonia alba used as ? X B- dioica S 

 gave plants either c? or ? (repeated by Bateson and Punnett, 

 giving equal numbers of the two sexes) ; but B. dioica ? X cî of 

 B. alba gave plants which were wholly ?. Our own similar crosses 

 gave the same result, with the exception of rare S flowers near the 

 base of the stem in occasional plants. All offspring of these matings 

 have, so far, proved absolutely sterile in both S and ? organs. 



Sexual differences may, apart from the manner of their trans- 

 mission, act in inter-relation with other factors, "letting off" characters 

 in one sex which are imperceptible in the other.-) For example 



^) Compare Biffen's case in Barley (12a). 



2) A phenomenon probably of this nature occurs in regard to „Tortoise-shell" 

 cats, which as is well known, are almost always female. Doncaster (5Ü) has given 

 reasons for the belief that such cats are heterozygotes of black and orange. These 

 heterozygotes are thus tortoise-shell in the case of females, and orange in the case 

 of males. 



