344 Doubleness in Stocks 



Mating 3. cZ-cream $ x no-d-iion-cvea,m ^. 



Summary of results. For details see Table V. 



Only one kind of mating of this type was made, viz. rf-glabrous 

 cream % x ??,o-d-glabrous white J". The d-cream plant M as % was 

 crossed with the no-cZ-white plant J as </", and two F, descendants of the 

 d-cream plant K as % were crossed with an F^ descendant of plant 

 J &B ^ (see pp. SU— 317 and Table II). Now plant K, it will be 

 recalled, was a sporting cream which gave excess of doubles, but 

 which was under suspicion of being a cross-bred cream since some of 

 its offspring appeared to breed true to singleness. At present therefore 

 we must accept the results obtained from this plant with some 

 reserve until they have been confirmed with material that is beyond 

 question. 



In accordance with expectation some F, families gave a mixture of 

 singles and doubles, others bred true to singleness. In the mixed F2 

 families the proportion of singles and doubles was evidently 3 s. : 1 d. 

 with one doubtful exception ; the bulk of the plants were singles with 

 white plastids and doubles with cream plastids, the former being in 

 excess, but a small proportion of singles with cream plastids, and 

 doubles with white plastids occurred in some cases. The F., families 

 containing ouly singles were composed almost exclusively of non-creams, 

 only 7 individuals in a total of 420 having cream plastids ; these 7 

 occurred in 2 F2 families derived from the suspected cream. 



Altogether 26 F^ plants were self-fertilised to produce Fo. 14 of 

 the F., families were mixed, 12 were composed only of singles. Although 

 two or three of these latter families are too small to put their purity 

 beyond doubt, and may therefore possibly cause the percentage of 

 all-single families to appear slightly higher than it actually is, the 

 result as it stands cannot be far from the truth, and agrees well with 

 the expectation of 7 -I- a; breeding true to 9 — a; giving both singles and 

 doubles. 



In the case of the mixed F^ families, the F-^ parent was presumably 

 derived from the union of 



xyw 

 or Xyw 

 or xYw ovules with XYW pollen 



and a scheme of gametogenesis which would give the observed result, 

 where all four forms occurred in F„, might be imagined thus in the 



