his view it
can only form two kinds of gametes, viz. Eb and eB, and these, of course,
will be formed in equal numbers. Such a plant on self-fertilisation must
give the zygotic series EEbb + 2 EeBb + eeBB, _i.e._ 1 erect red, 2 erect
purples, and 1 hooded purple. And because the erect reds and the hooded
purples are respectively homozygous for E and B, they must thenceforward
breed true. The erect purples, on the other hand, being always formed by
the union of a gamete Eb with a gamete eB, are always heterozygous for both
of these factors. They can, consequently, never breed true, but must always
give erect reds, erect purples, and hooded purples in the ratio 1 : 2 : 1.
The experimental facts are readily explained on the assumption of repulsion
between the two {92} factors B and E during the formation of the gametes in
a plant which is heterozygous for both.

Other similar cases of factorial repulsion have been demonstrated in the
sweet pea, and two of these are also concerned with the two factors with
which we have just been dealing. Two distinct varieties of pollen grains
occur in this species, viz. the ordinary oblong form and a rather smaller
rounded grain. The former is dominant to the latter.[7] When a cross is
made between a purple with round pollen and a red with long pollen the F_1
plant is a long pollened purple. But the F_2 generation consists of purples
with round pollen, purples with long pollen, and reds with long pollen in
the ratio 1 : 2 : 1. No red with round pollen appears in F_2 owing to
repulsion between the factors for purple (B) and for long pollen (L).
Similarly plants produced by crossing a red hooded long with a red round
having an erect standard give in F_1 long pollened reds with an erect
standard, and these in F_2 produce the three types, round pollened erect,
long pollened erect, and long pollened hooded, in the ratio 1 : 2 : 1. The
repulsion here is between the long pollen factor (L) and the factor for the
erect standard (E).

{93}

Yet another similar case is known in which we are concerned with quite
different factors. In some sweet peas the axils whence the leaves and
flower stalks spring from the main stem are of a deep red colour. In others
they are green. The dark pigmented axil is dominant to the light one.
Again, in some sweet peas the anthers are sterile, setting no pollen, and
this condition is recessive to the ordinary fertile condition. When a
sterile plant with a dark axil is