64 Double Petunias 



2. Cross-bred singles derived from one single and one double parent 

 also produce only singles when self-fertilised or fertilised inter se. 



3. Singles crossed with pollen from a double yield doubles in the 

 first generation. 



4. In families containing a mixture of singles and doubles, the 

 singles are in excess of the doubles. There is some evidence to show 

 that in some cases the ratio approximates to 9 s. : 7 d. and in others to 

 3 s. : 1 d. The occurrence of the ratio 9 s. : 7 d. in many of the cross- 

 bred families strongly suggests that more than one factor is concerned 

 in determining the occurrence of singles and doubles, and this view is 

 in harmony witii the conclusions formed in the case of Stocks. 



5. The male organs are functional in doubles, but the gynoecium is 

 more or less deformed, and when fertilised yields no seed, hence the 

 double character can only be introduced on the male side. 



6. Doubleness behaves as the recessive, singleness as the dominant 

 character. 



7. Gametogenesis is of the peculiar type which has already been 

 shown to occur in Matthiola, the factors for singleness and doubleness 

 being distributed differently among the ovules and the pollen grains. 



8. The pollen of the singles is homogeneous as regards the presence 

 of some factor essential to the manifestation of singleness. 



9. With regard to the constitution of the ovules of the singles and 

 the pollen of the doubles it may be said that the results obtained on 

 crossing are such as would occur, if either the ovules were homogeneous 

 and the pollen heterogeneous as regards the absence of some factor 

 needed to produce singleness ; or if conversely the ovules were hetero- 

 geneous and the pollen homogeneous in respect of this factor. The 

 fact that all the singles appeared capable of yielding doubles when 

 crossed with the pollen of a double points strongly to the first alternative, 

 but the impossibility of making reciprocal crosses renders direct proof 

 difficult. 



The expenses incurred in connection with these experiments have 

 been in part defrayed by a grant from the British Association for the 

 Advancement of Science. 



