COUPLING 199 
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 severa] days earlier 
than the second, the blossoms of which were purple. 
The F, plants (with purple blossoms) came into flower 
at a period intermediate between those of the parents. 
In F, 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 
