Fig. 21. Cross-fertilization of the Rattlesnake-Plantain. Side Sections
The further demonstration will be better shown by profile sections (Fig. 21). Nectar is secreted in the hollow of the lip indicated, somewhat as in the cypripedium. If we now imitate with a probe the habit of the insect and the action of its tongue, we may witness a beautiful contrivance for cross-fertilization. We will suppose the bee to be working at the top of the spike. He thrusts his tongue into the narrow opening (G). The membrane protecting the pollen-gland, thus surely touched, ruptures as described, and the exposed gland attaches itself to the tongue, being withdrawn as at H, and located on the insect's tongue, as in F, Fig. 20. The bee leaves this flower cluster and flies to another, upon which it will usually begin operation at the bottom. The flower thus first encountered is an old bloom, as in Fig. 19, D. Its sepals are more spreading, the lip slightly lowered, and the column so changed as to present the plane of the stigma, before out of sight, in such a new position as to invariably receive the pollen. The tongue of a bee entering this flower conveys the pollen directly against the stigmatic surface (I), which retains its disentangled fecundating grains, as at J, and the flower's functional adaptations are fulfilled.
Fig. 20. Cross-fertilisation of the Rattlesnake-Plantain. Front View
The Tongue of a Bumblebee
In the allied Spiranthes, or "Lady's-Tresses," a somewhat similar mechanism prevails, by which fertilization is largely effected by the changed position or angle of the stigma plane.
And thus we might proceed through all the orchid genera, each new device, though based upon one of the foregoing plans, affording its new surprise in its special modification in adaptation to its insect sponsor—all these various shapes, folds of petals, positions, colors, the size, length, and thickness of nectary, the relative positions of pollen and stigma, embodying an expression of welcome to the insect with which its life is so marvellously linked. Occasionally this astounding affinity is faithful to a single species of insect, which thus becomes the sole sponsor of the blossom, without whose association the orchid would become extinct. A remarkable instance of this special adaptation is seen in the great Angræcum orchid of Madagascar, described by Darwin; and inasmuch as this species glorifies Darwin's faith in the truth of his theory, and marks a notable victory in the long battle for its supremacy, it affords an inspiring theme for my closing paragraphs.
Among the host of sceptics—and were they not legion?—who met this evolutionary and revolutionary theory with incredulity, not to say ridicule or worse, was one who thus challenged its author shortly after the appearance of his "Fertilization of Orchids," addressing Darwin from Madagascar substantially as follows: "Upon your theory of evolution through natural selection all the various contrasting structural features of the orchids have direct reference to some insect which shall best cross-fertilize them. If an orchid has a nectary one inch long, an insect's tongue of equivalent length is implied; a nectary six inches in length likewise implies a tongue six inches long. What have you to say in regard to an orchid which flourishes here in Madagascar possessing a long nectary as slender as a knitting-needle and eleven inches in length? On your hypothesis there must be a moth with a tongue eleven inches long, or this nectary would never have been elaborated."