Page:Darwin - The various contrivances by which orchids are fertilized by insects (1877).djvu/279

. IX. tied together in the Ophreæ, and which run far up inside the waxy masses of the Vandeæ, are also of a different nature from the cementing matter; for the threads are acted on by chloroform and by long immersion in spirits of wine; whilst these fluids have no particular action on the cohesion of the waxy masses. In several Epidendreæ and Vandeæ the exterior grains of the pollen-masses differ from the interior grains, in being larger, and in having yellower and much thicker walls. So that in the contents of a single anther-cell we see a surprising degree of differentiation in the pollen, namely, grains cohering by fours, then being either tied together by threads or cemented together into solid masses, with the exterior grains different from the interior ones.

In the Vandeæ, the caudicle, which is composed of fine coherent threads, is developed from the semi-fluid contents of a layer of cells. As I find that chloroform has a peculiar and energetic action on the caudicles of all Orchids, and likewise on the glutinous matter which envelopes the pollen-grains in Cypripedium, and which can be drawn out into threads, we may suspect that in this latter genus,—the least differentiated in structure of all the Orchideæ,—we see the primordial condition of the elastic threads by which the pollen-grains are tied together in other and more highly developed species.