the act of crossing, we have good reason to believe (as will
hereafter be more fully alluded to), would produce very vigorous
seedlings, which consequently would have the best chance of flourishing
and surviving. Some of these seedlings would probably inherit the
nectar-excreting power. Those individual flowers which had the largest
glands or nectaries, and which excreted most nectar, would be oftenest
visited by insects, and would be oftenest crossed; and so in the
long-run would gain the upper hand. Those flowers, also, which had their
stamens and pistils placed, in relation to the size and habits of the
particular insects which visited them, so as to favour in any degree
the transportal of their pollen from flower to flower, would likewise be
favoured or selected. We might have taken the case of insects visiting
flowers for the sake of collecting pollen instead of nectar; and as
pollen is formed for the sole object of fertilisation, its destruction
appears a simple loss to the plant; yet if a little pollen were carried,
at first occasionally and then habitually, by the pollen-devouring
insects from flower to flower, and a cross thus effected, although
nine-tenths of the pollen were destroyed, it might still be a great gain
to the plant; and those individuals which produced more and more pollen,
and had larger and larger anthers, would be selected.

When our plant, by this process of the continued preservation or natural
selection of more and more attractive flowers, had been rendered highly
attractive to insects, they would, unintentionally on their part,
regularly carry pollen from flower to flower; and that they can most
effectually do this, I could easily show by many striking instances.
I will give only one--not as a very striking case, but as likewise
illustrating one step in the separation of the sexes of plants,
presently to be alluded to. Some holly-trees bear only male flowers,
which have four stamens producing rather a small quantity of pollen, and
a rudimentary pistil; other holly-trees bear only female flowers; these
have a full-sized pistil, and four stamens with shrivelled anthers, in
which not a grain of pollen can be detected. Having found a female
tree exactly sixty yards from a male tree, I put the stigmas of twenty
flowers, taken from different branches, under the microscope, and
on all, without exception, there were pollen-grains, and on some a
profusion of pollen. As the wind had set for several d