90 Reversion in Colour [ch. 



remarkable opportunity of studying a reversion in colour 

 due to crossing, for these plants instead of being white 

 were purple like the wild Sicilian plant from which our 

 cultivated sweet peas are descended. 



The facts respecting the colour inheritance will now be 

 given. With regard to the pollen-shape it must suffice at 

 present to state that the long shape is a dominant and the 

 round a recessive. The details as to the distribution of 

 these two shapes among the F^ individuals, which are 

 interesting and have greatly aided the development of 

 genetic theory, are given in the chapter dealing with the 

 phenomenon of *' gametic coupling." The present section 

 is concerned with colour only. 



When the reversionary F^ generation was first seen its 

 nature was entirely mysterious. When 7% was raised from 

 these F^ plants the series consisted of a mixture of plants, 

 some coloured and some white. In some cases the series 

 of coloured plants consisted of two kinds only, purples like 

 7^,, and a red bicolour type, the well-known old variety 

 called '* Painted Li^dv.'' 



In other cases F^ contained besides those mentioned, 

 two quite distinct additional types of purples and two 

 corresponding additional types of reds. 



The phenomena, though, as will be shown, in reality 

 very simple, presented superficially an appearance of great 

 complexity. Further difficulties were met with in the fact 

 which was soon discovered, that the cross between long- 

 pollened whites and round-pollened whites does not always 

 give the coloured types, but may result in ordinary whites 

 only. 



It is unnecessary to go through the long series of steps 

 by which the analysis of the phenomena was carried out. 

 The meaning of the facts is now perfectly clear and they 

 can all be arranged in one consistent scheme. 



Of the two white parents originally used the one 

 possessed one of the two factors we have called C and R, 

 the other introducing the other complementary factor. .The 

 meeting of these two elements produces colour in the fiower. 

 If no other epistatic factor is present their colour is red. As 

 a matter of experiment however one of the parents, proved 

 afterwards to be that which had the long pollen, did carry 



