COUPLING 187 



colour in these different situations doubtless depends 

 upon the presence of a particular pigment in the plant 

 which exhibits it. Nevertheless, we can scarcely 

 fail to look upon these three separate manifestations 

 of the pigment as representing distinct characters, and 

 this being so, we suppose their germinal representa- 

 tives to be coupled together in such a way that they 

 remain associated at the time when, during the forma- 

 tion of the germ-cells of the heterozygote, other allelo- 

 morphs become independently segregated. 



And this way of looking at the facts is further 

 justified by the behaviour of the characters in ques- 

 tion in another species of plant. For in the sweet pea 

 it is possible for the coupling between these characters 

 to be broken down, so that a plant which exhibits 

 green leaf axils may, under certain circumstances, bear 

 coloured flowers. In such a plant the leaf -axil-colour 

 and the flower-colour must clearly be represented by 

 independent allelomorphs. 



In other cases, again, there may be coupling between 

 characters which have no obvious relation to one 

 another at all. In illustration we may take the case 

 of a cross between two strains of peas, one of which had 

 white flowers and opened its buds several days earlier 

 than the second, the blossoms of which were purple. 



The Fj plants (with purple blossoms) came into flower 

 at a period intermediate between those of the parents. 

 In F 2 506 plants were grown successfully. Some of 

 these flowered as early as the white parent, and others 

 as late as the purple parent ; but the majority of the 

 plants ranged between these two extremes, so that it 



