316 Donbleness in Stocks 



is either equality or a slight excess of doubles. In the next generation 

 this diversity of behaviour was again apparent ; 3 F2 plants belonging 

 to 2 Fi families, both of which included some doubles, were tested 

 by cross-breeding. One was used as (/" in a mating with the rf-red 

 strain and gave a total of 36 all single. Another was employed 

 as the </ parent with two individuals of the eversporting sulphur- 

 white race and gave a total of 92 (58 -|- 34) offspring again all single. 

 The third individual, which was sister to the last-mentioned plant, and 

 was similarly used as the (/ parent in a mating with the same two 

 sulphur-white individuals and also with another sulphur-white plant 

 gave, on the other hand, a mixture of singles and doubles, the singles 

 in each case being largely in excess. These results may be summarised 

 thus : L itself yielded singles and doubles in the proportion of 3 s. : 1 d.; 

 when self-fertilised the resulting F^ singles pi'oved to be mixed, some 

 yielding again 3 s. : 1 d., others apparently breeding true to singleness ; 

 whether also some of the F^ singles were yielding a higher proportion 

 of doubles than 1 in 4 is not certain. In the F3 generation a similar 

 result was obtained, some of the F„ singles were evidentl}' breeding true 

 to singleness, while others gave an excess of singles when mated with 

 an eversporting form. 



There remain the plants M and X about which all that can be said 

 is that both were evidently able to throw doubles, but whether in excess, 

 or not, there is not sufficient evidence to determine. 



Among the various matiugs of the cream race with other forms, only 

 two happened to be carried out in such a way as to enable the double- 

 throwing character of the pollen to be tested independently of the 

 ovules as is the case when a )jo-rf-strain is used as the $ parent in the 

 cross. 16 of the F^ plants resulting from these two unions were self- 

 fertilised, viz., 1 Fj from the mating no-d-Qesh $ x rf-cream (plant X) 

 (/■ and 15 from no-d-white $ x d-cream (plant H) j/*, and each yielded 

 doubles in the next generation. The total number of pollen grains 

 belonging to the two non-sap-coloured forms, which were tested in this 

 way, is then 20 from the white race (see p. 314) and 16 from the cream, 

 and all proved to be carrying the double character. 



We find then that seed of the double-throwing strains of white and 

 cream, as supplied commercially, appears to differ from similar seed of 

 the sap-coloured races in that it is not homogeneous. Though the plants 

 raised are uniform and true to type in respect of other characters such 

 as flower colour and character of leaf surface, they differ in behaviour as 

 regards the double-throwing characters. They behave in fact as we 



