S06 Doubleness in Stocks 



and creams. From independent experiments' we know that white 

 plastid colour is dominant to cream, nevertheless among the offspring 

 of the sulphur-whites the dominant whites are not more numerous than 

 the recessive creams. Moreover the inheritance of plastid colour is 

 curiously bound up with the inheritance of singleness and doubleness ; 

 for whereas in the sulphur-white race the singles, so far as experiment 

 has yet gone, are all white, the doubles are for the most part cream, 

 though a few are white like the singles. It was with the aim of 

 elucidating these phenomena that the present experiments were under- 

 taken, and in the following account I have attempted to show that by a 

 conception of coupling and repulsion^ among the factors, and a peculiar 

 but definite distribution of the factors among the reproductive cells de- 

 pending upon their sex, these hitherto unexplained facts can be related 

 to our previous knowledge, and brought together into a general scheme. 



Later experiments on the inheritance of "doubleness" 

 and plastid colour. 



I. Races which were obtained only in the double-throwing form. 

 Two of the Ten-week wallflower-leaved varieties, viz. red (crimson) 

 and sulphur-white, appear to be obtainable only in the double-throwing 

 form. Direct proof of the eversporting character is obtained if doubles 

 are always found to occur when individuals of the race in question are 

 self-fertilised, while corroborative evidence is afforded by the indirect 

 method of crossing. For if the conclusion in regard to the character of 

 the pollen grains in eversporting races given above (p. 304) be correct, 

 it follows (1) that when an eversporting race is used as the pollen 

 parent in a cross with a true-breeding (no-d) race, doubles, though 

 absent in Fi, may be expected to occur in every family in F..; (2) that 



' Rep. Evol. Committee, IV, 1908, p. 3,5. 



- The terms coupling and repulsion have been employed by Bateson and Punnett in 

 explanation of certain results obtained by them in the Sweet Pea, which seemed to 

 suggest that the inter-relation between certain factors was of the nature of attraction or 

 repulsion according as these factors were received separately from the parents or 

 associated together (see Proc. Roy. Soc. B, Vol. 84, 1911). In a later communication 

 which appeared after the present paper had been sent to press (see Verhandltmgen des 

 naturforschendeii Vereines in Briinn, Bd. xlix. and also the present number of this Journal 

 of Genetics), these authors suggest the substitution of the general expression "reduplica- 

 tion of terms " to cover both cases. Pending the acceptance of other terms which will 

 serve to distinguish results which would have been classed under the head of coupling 

 from those coming under the head of repulsion the original terms are here retained, as 

 conveniently descriptive of the two types of results, not as connoting necessarily the real 

 cause of the phenomena. 



