340 Doableness in Stocks 



together the numbers obtained in the 9 mixed families in the last 

 experiment (see Table V), we get a total of 



371 s. and 115 d., 



where a ratio of 3 s. : 1 d. would give 



364-5 s. : 121-5 d. 



Though in two of the families the proportion of doubles was 

 distinctly less than 1 in 4, it seems more likely, on the whole, that 

 these are cases of accidental variation in the direction of deficiency 

 fi-om the ratio 3 s. : 1 d., than that they represent some considerably 

 higher ratio such as evidently occurs in certain other matings. 

 Assuming the constitution given above we may suppose that in the 

 gametogenesis of F^ an equal number among the pollen and the 

 ovules carry the combinations XYW and xyW (or XyW or xYW as 

 the case may be). The gametic types would be simply expressed 

 thus 



Ovules Pollen 



XYW XYW 



xyW xyW 



in the case of an F^ plant derived from an xy ovule, a corresponding 

 substitution being made in the case of an F^^ plant derived from an 

 Xy or an xY ovule. This being so, we should expect the same result 

 in F^ from the F^ singles, as was obtained in F., from the -f, plants ; 

 and this was the case. Of three Fo sister plants which were self- 

 fertilised, two gave a mixture in a proportion approximating to 

 3 s. : 1 d. (viz. 20 s., 9 d. and 5 s., 2 d. respectively) and one gave 

 a family of 21 all single. 



The F„ families composed entirely of singles will have been pro- 

 duced by those jP, plants which were derived from the union of XYW 

 ovules and XYW pollen. In all these families the double character 

 will have been bred out completely, so that not only will doubles be 

 absent in them, but they will be wanting in all later generations 

 derived from such F^, families. Confirmatory evidence of this fact was 

 obtained both in F^ and Ft, after which the experiment was brought to 

 an end. The F-^ generation was raised from 41 self-fertilised F„ plants 

 belonging to 11 out of the 16 all-single families, and consisted of 898 

 plants all of which were single. In F^ seven families numbering all 

 together 77 individuals were again all single. 



We may now consider the reciprocal cross. 



