Page:Darwin - The various contrivances by which orchids are fertilized by insects (1877).djvu/161

. V. represented sideways in fig. B, and frontways in fig. C. By this springing action the anther scoops the pollinium out of the concave clinandrum, and pitches it up in the air, with exactly the right force so as to fall down on the middle of the viscid stigma, where it adheres.

Under nature, however, the action cannot be as thus described, for the labellum hangs downwards; and to understand what follows, the drawing should be placed in an almost reversed position. If an insect failed to remove the pollinium by means of the viscid matter from the rostellum, the pollinium would first be jerked downwards on to the protuberant surface of the labellum, placed immediately beneath the stigma. But it must be remembered that the labellum is elastic, and that at the same instant that the insect, in the act of leaving the flower, lifts up the lip of the anther, and so causes the pollinium to be shot out, the labellum will rebound back, and striking the pollinium will pitch it upwards, so as to hit the adhesive stigma. Twice I succeeded in effecting this by imitating the retreat of an insect, with the flower held in its natural position; and on opening it, found the pollinium glued to the stigma.

This view of the use of the elastic filament, seeing how complicated the action must be, may appear fanciful; but we have seen so many and such curious adaptations, that I cannot believe the strong elasticity of the filament and the thickening of the middle part of the labellum to be useless points of structure. If the action be as I have described, we can perceive their meaning, for it would be an advantage to the plant that its single large pollen-mass should not be wasted, supposing that it failed to adhere to an insect by means of the viscid matter from the rostellum.