E. R. Saunders 



325 



scheme suggested above (p. 323), according to which the distribution 

 of the factors for singleness and doubleness is assumed to be the same 

 for all eversporting forms. We should naturally expect that a condi- 

 tion which obtains in both parents would also hold good in their 

 cross-bred offspring, and we may therefore conclude that, so far as the 

 factors for singleness and doubleness are concerned, the general scheme 

 of segregation in ^i cross-breds derived from two eversporting forms 

 will be the same as that put forward in the case of the parents (see 

 p. 322). 



The distribution of plastid colour needs further consideration, since 

 in respect of this character reciprocal cross-breds from unions between 

 eversporting cream and non-cream forms give different results. Matings 

 of this type can be carried out in six different ways as shown below, 

 where the unions 2, 4 and 6 are the reciprocals of 1, 3 and 5. 



Mating 1 d-snlphar -white ? x d-non-cream i 



2 (2-non-cream ; x d-salphor-white g 



3 d-non-cream 2 x d-cream ^ 



4 d-cream ? x d-non-cream ^ 



5 d-8ulphur- white ? x d-cream <f 



6 d-cream ? x d- sulphur-white <f 



The composition of the ovules and pollen uniting to produce the 

 single plants in F^ according to the scheme given above, together with 

 a general statement of the results obtained in F. for those cases which 

 have already been carried out, is given below. 



Mating 



1 



2 

 8 



Constitution of the gametes 



anitiog to produce the 



single plants in fi 



Results obt&ined in F« 



Omles 



XYW 

 XTW 

 XYW 



XYw 



XTW 

 XYw 



Pollen 



xyW 



xyw 



xyw 



xyW 



xyw 



xyw 



Singles 



with white 



plastids 



many 



many 



(a) many 



(b) many 



Singles 



with cream 



plastids 



Doubles Doubles 



with white with cream 



plastids plastids 



none many 



(not yet carried out) 

 none none 



few many 



few many 



(not yet carried out) 

 (not yet carried out) 



many 



none 



few(?) 



Only three of these matings have as yet been carried to F^. It is 

 doubtful however whether the results of unions 2, 5 and 6, when 

 available, will throw any further light on the relation existing between 

 plastid colour and singleness and doubleness, since we may suppose 



Joum. of Oen. i 22 



