ays from the
female to the male tree, the pollen could not thus have been carried.
The weather had been cold and boisterous, and therefore not favourable
to bees, nevertheless every female flower which I examined had been
effectually fertilised by the bees, accidentally dusted with pollen,
having flown from tree to tree in search of nectar. But to return to
our imaginary case: as soon as the plant had been rendered so highly
attractive to insects that pollen was regularly carried from flower
to flower, another process might commence. No naturalist doubts the
advantage of what has been called the "physiological division of
labour;" hence we may believe that it would be advantageous to a plant
to produce stamens alone in one flower or on one whole plant, and
pistils alone in another flower or on another plant. In plants under
culture and placed under new conditions of life, sometimes the male
organs and sometimes the female organs become more or less impotent;
now if we suppose this to occur in ever so slight a degree under nature,
then as pollen is already carried regularly from flower to flower,
and as a more complete separation of the sexes of our plant would be
advantageous on the principle of the division of labour, individuals
with this tendency more and more increased, would be continually
favoured or selected, until at last a complete separation of the sexes
would be effected.

Let us now turn to the nectar-feeding insects in our imaginary case: we
may suppose the plant of which we have been slowly increasing the nectar
by continued selection, to be a common plant; and that certain insects
depended in main part on its nectar for food. I could give many facts,
showing how anxious bees are to save time; for instance, their habit of
cutting holes and sucking the nectar at the bases of certain flowers,
which they can, with a very little more trouble, enter by the mouth.
Bearing such facts in mind, I can see no reason to doubt that an
accidental deviation in the size and form of the body, or in the
curvature and length of the proboscis, etc., far too slight to be
appreciated by us, might profit a bee or other insect, so that an
individual so characterised would be able to obtain its food more
quickly, and so have a better chance of living and leaving descendants.
Its descendants would probably inherit a tendency to a similar slight
deviation of structure. The tubes of the corollas of the common red and
incarnate clove