E. R. Saunders 333 



the ovules can only be certainly determined by breeding to F^, since 

 the result in F^ will be the same (or almost the same) whatever be the 

 proportion of ovules containing W to those lacking it. 



We may surmise however from the behaviour of the cross-breds in 

 the reciprocal union that most (if not all) of the ovules carrying single- 

 ness will lack W, and conversely that W will be present in most (if not 

 all) of those which carry doubleness. There seems in fact strong reason 

 to suppose that in matings between eversporting forms of unlike plastid 

 colour, the plastid colour allelomorphs are associated in F^, chiefly or 

 exclusively, the one with singleness the other with doubleness according 

 as each is associated with singleness or doubleness in the germ cells 

 which united to produce F^. 



The cream plant used as the seed-parent in experiment (b) was 

 a descendant of plant K, an individual which yielded an excess of 

 doubles on self-fertilisation but which nevertheless is under suspicion 

 of not having been a genuine eversporting type, since some of its 

 offspring were found to breed true to singleness (see p. 315). This 

 being so, it is not improbable that this particular descendant of K was 

 also not genuinely eversporting but some form of cross-bred. It is 

 therefore at present uncertain whether we shall be right in ascribing 

 the appearance of the one single with cream plastids in the case of the 

 (6) mating to the spurious character of the cream plant used as the 

 $ parent in this case, or whether we are to suppose that this form 

 would also have appeared in the (a) results if a larger sowing had been 

 made. For it is not certain that a total of 185-1-328 = 513 plants, 

 recorded when the cream plants G and H were used, is sufficiently large 

 to exhibit the complete series in Fo. 



We may then state the conclusions in regard to matings between 

 eversporting forms thus : 



1. Segregation in F^ cross-breds from two eversporting forms follows 

 the same course as in the eversporting parents, so far as the factors 

 X and Y are concerned. (See above, p. 320, where it is shown that 

 cross-breeding and inter-breeding between these forms give the same 

 proportion of singles and doubles.) 



2. If the eversporting parents are of unlike plastid colour, all or 

 almost all the F-^ pollen carries the same allelomorph for plastid colour 

 as the pollen which was used to produce F^; similarly, the other member 

 of the pair, which is borne only or chiefly by the ovules, is borne only 

 or chiefly by those ovules carrying the same combination of factors as 

 the ovule from which the F^ plant in question was derived, viz. the 



