Page:Darwin - The various contrivances by which orchids are fertilized by insects (1877).djvu/206

186 balls of pollen, and tearing the loosely attached spike-like anther from the top of the column. The pollinium is always ejected with its viscid disc foremost. I imitated the action with a minute strip of whalebone, slightly weighted at one end to represent the disc; this was then bent half round a cylindrical object, the upper end being at the same time gently held by the smooth head of a pin, to represent the retarding action of the anther, the lower end was then suddenly set free, and the whalebone was pitched forward, like the pollinium of the Catasetum, with the weighted end foremost.

That the disc is first jerked out of the stigmatic chamber, I ascertained by pressing the middle of the pedicel; and when I touched the antenna the disc instantly sprung forth, but, owing to the pressure on the pedicel, the pollinium was not dragged out of the anther-cell. Besides the spring from the straightening of the pedicel, elasticity in a transverse direction comes into play: if a quill be split lengthways, and the half be forced longitudinally on a too thick pencil, immediately the pressure is removed the quill jumps off; and an analogous action takes place with the pedicel of the pollinium, owing to the sudden inward curling of its edges, when set free. These combined forces suffice to eject the pollinium with considerable force to the distance of two or three feet. Several persons have told me that, when touching the flowers of this genus in their hothouses, the pollinia have struck their faces. I touched the antennæ of C. callosum whilst holding the flower at about a yard's distance from a window, and the pollinium hit the pane of glass, and stuck by its adhesive disc, to the smooth vertical surface.

The following observations on the nature of the