ed, we should
expect the F_2 generation to consist of the four forms: erect purple,
hooded purple, erect red, and hooded red in the ratio 9 : 3 : 3 : 1. Such,
however, is not the case. The F_2 generation {90} actually consists of only
three forms, viz. erect red, erect purple, and hooded purple, and the ratio
in which these three forms occur is 1 : 2 : 1. No hooded red has been known
to occur in such a family. Moreover further breeding shows that while the
erect reds and the hooded purples always breed true, the erect purples in
such families _never_ breed true, but always behave like the original F_1
plant, giving the three forms again in the ratio 1 : 2 : 1. Yet we know
that there is no difficulty in getting purple bicolors to breed true from
other families; and we know also that hooded red sweet peas exist in other
strains.

Painted Lady x Duke of Westminster
(erect red) | (hooded purple)
|
Purple Invincible
(erect purple)
|
+-------------+-----------------+
| | |
Painted Purple Invincible Duke of
Lady Westminster
(1) (2) (1)

EEbb eeBB Parents
/\ /\
/ \ / \
/ \ / \
Eb Eb eB eB gametes
\------------/
EeBb F_2
____/ \____
/ \
Fem. gametes of F_1 Eb ---> EEbb <--- Eb Male gametes of F_1
Eb ---> EeBb <--- eB
eB ---> EeBb <--- Eb
eB ---> eeBB <--- eB
\----/
F_2 generation

On the assumption that there exists a repulsion between the factors for
erect standard and blue in a plant which is heterozygous for both, this
peculiar case receives a simple explanation. The constitutions of the erect
red and the hooded purple are EEbb and eeBB respectively and that of the
F_1 erect purple is EeBb. Now let us suppose that in such a zygote there
exists a repulsion {91} between E and B, such that when the plant forms
gametes these two factors will not go into the same gamete. On t