The horse-chestnut blossoms also cooperate. The pyramidal bunch of bloom is not a crowd of individuals each self-contained and self-sufficient. It is more like the ant and bee communities, in which each individual has duties to be performed for the good of all.
Most of the white blossoms, flecked with rose or gold, have no individual future. Their prospects are sunk for the public good. They have no pistils and will ripen no seed.
Their prettiness is merely a lure to attract some flying insect to the spire of bloom. She will carry away their pollen, for which they can receive no return in kind, as they have no stigmas and can set no seed. And having been enticed to the boughs by them, and bearing their powdered gold on her body, she will visit some sister-flower, which is in botanical language "perfect," and from which will develop, later, the horse-chestnut bur.
On the blooming spire there are scores of flowers, but if we look at the branch again, in later summer, we will see that only six or eight of them have set their seed. The rest have perished, as the worker-ants do, leaving no descendants; the only memento of their lives will be the work done for the community into which they were born.
The perfect blossoms of the horse-chestnut grow near the base of the spire of bloom. Their friend, the bee, works from the ground upward, and all the bee-flowers, which grow in spikes or bunches, have adapted themselves to this habit of their favorite messenger.
When she comes to a branch of horse-chestnut blossoms she is probably already dusted with pollen from another cluster. With this she flies to the lowest flowers of the spire, which are pistil-bearing, and therefore want pollen and have a use for it. Then, rising into the top of the spire, she takes on a fresh load of pollen from the stamenbearing flowers there, and when she visits another spire of bloom this will be carried to its lowest blossoms, which are pistillate.
Besides the perfectly developed pistil these lower flowers bear a number of stamens which, according to Dr. Ogle, never open, and never shed their stores of pollen. And the upper flowers, which nowadays do nothing except produce pollen and make a brave show, hold in their hearts little green rudiments which are significant signs of abandoned habits.
For each of these is a pistil almost dwindled to nothingness - a reminiscence of the time when the horse-chestnut flowers had not yet learned cooperation.
The long stamens of these topmost flowers have an upward curve which brings their anthers against the hairy hinder parts of their favorite visitor, the bumble-bee. And when the insect flies to the lower florets of the next spire, the long, curving pistils touch the same spot on her body and receive the pollen they need.
When the upper flowers of the spire have given away all their pollen they fall and strew the ground beneath the trees. The horse-chestnuts are cousins to the maples, and are not even distantly related to the chestnuts, which they resemble only in dependence upon the ministrations of insects and in the custom of late blooming.
For the chestnuts, too, blossom much later than most of the forest-trees, hanging out long, pollen-bearing flower-clusters, which are odorous and conspicuous to lure the flies, upon whose ministrations the life of the species depends.
The heavy scent of the blossoms is unpleasant to most people, but we are not the individuals concerned in the case. The faint suggestion of putridity is attractive to the many flies which hum around the branches in the warm June sunshine. They dust their bodies with pollen from the creamy spires, and then carry the life-giving dust to the pistillate flower-cluster, which ripens, later, into the chestnut-bur and its contents.
The prickly bur is developed from a little circle of scales which has surrounded a pair or a trio of pistillate flowers. Each chestnut is a ripened ovary, and the little tail atop is the remains of the style and stigma.
It is surmised that the chestnut flowers, like those of the ash-trees, once had both stamens and pistils, alike perfect in development, so that each blossom produced both pollen and ovules. What seems a reminiscence of such a condition of things is still to be seen in the pistil-bearing flowers; for each has from five to twelve "abortive" stamens - undeveloped things which are of no use in the trees' present domestic economy, but which are still produced, probably from sheer force of habit.