this form, and had, therefore, to pass it down between the anthers seated round
the mouth of the corolla, some pollen was almost invariably carried down and
left on the stigma. Minute insects, such as Thrips, which sometimes haunt the
flowers, would likewise be apt to cause the self-fertilisation of both forms.

The several foregoing facts led me to try the effects of the two kinds of pollen
on the stigmas of the two forms. Four essentially different unions are possible;
namely, the fertilisation of the stigma of the long-styled form by its own-form
pollen, and by that of the short-styled; and the stigma of the short-styled form
by its own-form pollen, and by that of the long-styled. The fertilisation of
either form with pollen from the other form may be conveniently called a
LEGITIMATE UNION, from reasons hereafter to be made clear; and that of either
form with its own-form pollen an ILLEGITIMATE UNION. I formerly applied the term
"heteromorphic" to the legitimate unions, and "homomorphic" to the illegitimate
unions; but after discovering the existence of trimorphic plants, in which many
more unions are possible, these two terms ceased to be applicable. The
illegitimate unions of both forms might have been tried in three ways; for a
flower of either form may be fertilised with pollen from the same flower, or
with that from a another flower on the same plant, or with that from a distinct
plant of the same form. But to make my experiments perfectly fair, and to avoid
any evil result from self-fertilisation or too close interbreeding, I have
invariably employed pollen from a distinct plant of the same form for the
illegitimate unions of all the species; and therefore it may be observed that I
have used the term "own-form pollen" in speaking of such unions. The several
plants in all my experiments were treated in exactly the same manner, and were
carefully protected by fine nets from the access of insects, excepting Thrips,
which it is impossible to exclude. I performed all the manipulations myself, and
weighed the seeds in a chemical balance; but during many subsequent trials I
followed the more accurate plan of counting the seeds. Some of the capsules
contained no seeds, or only two or three, and these are excluded in the column