312 



Doubleness in Stocks 



s 



(a) Sap-coloured races. 

 i. Evidence from self-fertilisation. 

 The number of individuals tested in each case is shown below 



Number of Individuals Tested. 



Totals 



16 



54 



22 



1 108 



Twelve individuals belonging to different sap-coloured forms were 

 taken at random, and they and 90 of tlieir descendants were self- 

 fertilised. Doubles were obtained from each of these 108 plants. (For 

 details see Table III.) Thus the evidence, so far as experiment has yet 

 gone, indicates that the double-throwing strains of these forms now on 

 the market are similar to the red and sulphur-white races in that they 

 are genuinely eversporting, and that it is iu fact impossible to breed 

 out the doubles. 



ii. Evidence from cross-breeding. 



To obtain the further proof that the double character is being 

 carried by all the pollen in each of these sap-coloured strains necessi- 

 tates the raising of a large number of F„ plants which iiave been bred 

 by self-fertilisation from the mating no-d $ x d (/' where the (/* parent 

 belongs to the sap-coloured form which is to be tested. 



Up to the present 36 F^ plants representing as many pollen grains 

 contributed by 6 c?-parents have been tested in this wa}'. The 

 parentage of these F^ plants and the number of pollen grains tested 

 in the case of each parent are shown below ; the composition of the F^ 

 families will be discu.ssed later (see p. 336 and Table IV) ; those marked 

 thus * have already been recorded (see Report II, p. 37). 



