Page:On the Various Contrivances by Which British and Foreign Orchids are Fertilised by Insects, and on the Good Effects of Intercrossing.djvu/50

anther, and as the matter from the rostellum is not highly viscid, they were sometimes left behind and not caught.

Owing to the inclination of the base of the clinandrum, and owing to the length and elasticity of the filament, when the anther was lifted up it was always shot over the rostellum, and remained hanging there, with its lower empty surface (Fig. C) suspended over the summit of the stigma. The filament now stretches across the space (see Fig. B) which was originally covered by the anther. Several times, having cut off all the petals and labellum, and laid the flower under the microscope, I raised with a needle the lip of the anther, without disturbing the rostellum, and saw the anther assume, with a spring, the position represented sideways in Fig. B, and frontways in Fig. C. By this springing action the anther scoops the pollen-mass 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 sticks.

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 nearly upside down, 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 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, lifted up the lid of the anther, and so caused the pollen-mass to be shot out, the labellum would rebound back, and striking the pollen-mass would pitch it upwards, so as to hit the sticky stigma. Twice I succeeded in effecting this, with the flower held in its natural position, by imitating the retreat of an insect; and on opening the flower I found the pollen-mass 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 of the labellum to be useless points of structure. If the action be as I have described, it might be an advantage to the plant that its single large pollen-mass should not be wasted, if it failed to adhere to an insect by means of the viscid matter from the rostellum. This contrivance is not common to all the species of the genus; for in neither D. bigibbum nor D. formosum was the filament of the anther elastic, nor was the middle line of the labellum thickened. In D. tortile the filament was elastic; but as I saw only one flower, before I had made out the structure of D. chrysanthum, I cannot say how it acts.

VANDEÆ