R. P. Gregory 83 



This would seem to imply the presence of some disturbing cause 

 affecting the regular Meudelian distribution, but it is important to 

 ascertain what reliance may be placed on the ratio determined from 

 the sum of all the families taken together. If the total results be 

 tested by the discordance of the results in the individual families which 

 make up the total \ it is found that, in the case of the (DR x DR) 

 crosses the approach to the normal 3 : 1 ratio is close, the observed 

 result being 29 1 ± "09 : 1 (Table, p. 81). In the (DR x R) and 

 (R X DR) crosses the observed result is 1-23 + lO : 1 (Table, p. 82) 

 the theoretical ratio for 724 plants being 10 + 01 : 1. 



Examined in this way, the results obtained at present perhaps 

 scarcely afford a clear indication as to whether the above noted diver- 

 gences are to be regarded as merely accidental, or whether they may 

 have some significance in regard to the observed differences in the 

 relative fertilities of the various kinds of legitimate and illegitimate 

 unions. 



Any significance, which the foregoing results may have in this connexion, lies in the 

 possibility that the observed differences in the fertility of the legitimate and illegitimate 

 onions^ may be, in part, due to differences in the fertility of the various kinds of gametic 

 anions, or rather (since the results of the matings (DR x R) and (R x DR) are in sub- 

 stantial agreement) to differences in the mortality of the three kinds of zygotes arising 

 from these unions. 



All the experiments on relative fertility are in agreement in showing that the union 

 (short-styled plant x short-styled plant) is distinctly the least fertile, while the legitimate 

 unions are the most fertile. Assuming that all forms of gametic union are equaUy 

 fertile, the cross (DR x DR) would give offspring in the proportion 1 DD : 2 DR : 1 RR 

 while the cross (DR x jR) would give 1 DR : 1 RR. But if there are differences in the 

 fertility of the various kinds of gametic union, the observed deficiency of short-styled 

 offspring in the cross (DR x DR) might be due to the small number of pure short -styled 

 plants which are produced, while the excess of short-styled offspring in the cross (DR x R) 

 might be due to greater fertility of the union (D x R) as compared with that of the union 

 (R X R). 



1 I am greatly indebted to Mr F. J. M. Stratton, of Gonville and Cains College, 



Cambridge, for this method of examining the results. 



^ See Darwin, Forms of Flowers, pp. 38 — 43, 246. Darwin found that the ratio of the 

 fertility of the two legitimate unions taken together to that of the two illegitimate unions 

 was 100 : 53. With this ratio that given by my experiments agrees very closely, but the 

 fertility of the long-styled form, whether fertilized by its own or by the other form of pollen, 

 is greater in the case of my plants than that observed by Darwin. The figures are 



Long X Short Short x Long Long x Long Short x Short 

 Average number of seeds per capsule 33 25 21 11 



It is to be presumed that the short-styled plants used by Darwin and Hildebrand 

 included, like mine, heterozygoos as well aa pore individuals. 



