E. R. Saunders 339 



Details of the several matings. 



i. The parents are alike in plastid colour, and are homozygous as 

 regards the allelomorph concerned ( W or w). 



Mating 1. d-cream $ x ?io-t^-cream j/". Not yet carried out. 



Mating 7 (reciprocal cross). ?io-d-cream $ x c?-cream (/". Not yet 

 carried out. 



Mating 2. tZ-non-cream $ x Ho-cZ-uon-cream ^. 



As stated above (p. 336) the expectation in such eases is that of the 

 Fj plants, some will breed true to singleness, and some will yield both 

 singles and doubles in F^- The results of several matings of this type 

 have already been recorded'. More recently another experiment of 

 this kind has been carried out on a considerably larger scale. The two 

 sets of results are summarised below : 



§§■3 o|| 'o-ggg.s 



='■3.5 J. * fe, .- 3 „ 



a*.-" Soo— s 01 g g^ 



Parental Types go ||.g sg^-so 



& 3. 



^<J-glabrous red $ x 7io-d-hoa,ry white {incana) J 1 



-d-glabrous flesh ? x ,, ,, ,, j 1 



^d-glabrous dark purple ? x »io-(Z-glabrous white <r 2 1 



^d-glabrous copper ? x ?io-rf-glabrouB flesh <f 1 



^i-glabrous dark purple ? x no-rf-glabrous light purple i 1 



d-glabrous red ? x no-d-glabrous white s 25 16 9 



Totals 31 17 14 



Altogether 31 Fi plants luere tested; 14 yielded singles and doubles in 

 Fo ivhile 17 gave only singles, where the expectation would be an almost 

 corresponding excess the other way, i.e. a proposition of 15 breeding 

 true : 17 which give doubles^. Experience has shown however in the case of 

 another character, viz. hoariness and smoothness, that where the expecta- 

 tion is as near equality as in this case a corresponding excess on the 

 wrong side is within the range of variation which we may expect. 



With regard to the proportion of singles and doubles in the mixed 

 Fn families it seems probable that the plants used as parents were true 

 to type in constitution (viz. XYxy and XYXY respectively) and that 

 the real ratio in every mixed family in F^ was 3 s. : 1 d. If we add 



' Reports to the Evolution Committee. 



2 Recorded in Report II, p. 37. 



* On the assumption, i.e. that the gametic series is on a 15 : 1 basis, see p. 322. 



