Page:Darwin - The various contrivances by which orchids are fertilized by insects (1877).djvu/44

24 game; and the trap so complex and perfect, with its symmetrical lines of rupture forming the saddle-shaped disc above, and the lip of the pouch below; and, lastly, this lip so easily depressed that the proboscis of a moth can hardly fail to uncover the viscid disc and adhere to it. But if this fails to occur, the elastic lip rises and covers again the viscid surface, so as to keep it damp. The viscid matter within the rostellum is attached to the saddle-shaped disc alone, and is surrounded by fluid, so that it does not set hard till the disc is withdrawn. The upper surface of the saddle, with the attached caudicles, is also kept damp by the bases of the anther-cells, until it is withdrawn, and then the curious clasping movement instantly commences, causing the pollinia to diverge, followed by the movement of depression, which movements together are exactly fitted to cause the ends of the two pollen-masses to strike the two stigmatic surfaces. These stigmatic surfaces are not so sticky as to tear off the whole pollinium from the proboscis of the moth, but by rupturing the elastic threads to secure a few packets of pollen, leaving plenty for other flowers.

But let it be observed that, although the moth probably takes a considerable time to suck the nectar of a flower, yet the movement of depression in the pollinia does not commence (as I know by trial) until they are fully withdrawn; nor will the movement be completed, and the pollinia properly placed for striking the stigmatic surfaces, until about half a minute has elapsed, which will give ample time for the moth to