What is the advantage gained in the pea-shaped blossom? As usual,
the insect that fertilizes the flower best knows the answer. The
corolla has five petals, the upper one called the standard,
chiefly a flaunted advertisement; two side wings, or platforms,
to alight on; and a keel like a miniature boat, formed by the two
lower petals, whose edges meet. In this the pistil, stamens, and
nectar are concealed and protected. The pressure of a bee's
weight as he alights on the wings, light as it must be, is
nevertheless sufficient to depress and open the keel, which is
elastically affected by their motion, and so to expose the pollen
just where the long-lipped bee must rub off some against his
underside as he sucks the nectar. He actually seems to pump the
pollen that has fallen into the forward part of the keel upon
himself, as he moves about. As soon as he leaves the flower, the
elastic wings resume their former position, thus closing the keel
to prevent waste of pollen. Take a sweet pea from the garden,
press down its wings with the thumb and forefinger to imitate the
action of the bee on them; note how the keel opens to display its
treasures, and resumes its customary shape when the pressure is
removed.

The lupine is another of those interesting plants which go to
sleep at night. Some members of the genus erect one half of the
leaf and droop the other half until it becomes a vertical instead
of the horizontal star it is by day. Frequently the leaflets
rotate as much as 90 degrees on their own axes. Some lupines fold
their leaflets, not at night only, but during the day also there
is more or less movement in the leaves. Sun dial, a popular name
for the wild lupine, has reference to this peculiarity. The leaf
of our species shuts downward around its stem, umbrella fashion,