Page:Darwin - The various contrivances by which orchids are fertilized by insects (1877).djvu/40

20 When the lip is depressed, the under and viscid surface of the disc, still remaining in its proper place, is uncovered, and is almost certain to adhere to the touching object. Even a human hair, when pushed into the nectary, is stiff enough to depress the lip or pouch; and the viscid surface of the saddle adheres to it. If, however, the lip be pushed only slightly, it springs back and recovers the under side of the saddle.

The perfect adaptation of the parts is well shown by cutting off the end of the nectary and inserting a bristle at that end; consequently in a reversed direction to that in which moths insert their proboscides; and it will be found that the rostellum may easily be torn or penetrated, but that the saddle is rarely or never caught. When the saddle together with the pollinia is removed on a bristle, the under lip instantly curls closely inwards, and leaves the orifice of the nectary more open than it was before; but whether this is of much service to the moths which frequent the flowers, and consequently to the plant, I will not pretend to decide.

Lastly, the labellum is furnished with two prominent ridges (l′, figs. A, B), sloping down to the middle and expanding outwards like the mouth of a decoy; these ridges serve to guide any flexible body, like a fine bristle or hair, into the minute and rounded orifice of the nectary, which, small as it already is, is partly choked up by the rostellum. This contrivance of the guiding ridges may be compared to the little instrument sometimes used for guiding a thread into the fine eye of a needle.

Now let us see how these parts act. Let a moth insert its proboscis (and we shall presently see how frequently the flowers are visited by Lepidoptera)