Page:Darwin - The various contrivances by which orchids are fertilized by insects (1877).djvu/165

. V. tubular, and its lower part is produced into a nectary, which penetrates the ovarium.

Now for the action of these parts. If any body of size proportional to that of the tubular flower be forced into it—a dead humble-bee acts very well—the tongue-shaped rostellum is depressed, and the object often gets slightly smeared with viscid matter; but in withdrawing it, the rostellum is upturned, and a surprising quantity of viscid matter is forced over the edges and sides, and at the same time into the lip of the anther, which is also slightly raised by the upturning of the rostellum. Thus the protruding tips of the caudicles are instantly glued to the retreating object, and the pollinia are withdrawn. This hardly ever failed to occur in my repeated trials. A living-bee or other large insect alighting on the fringed edge of the labellum, and scrambling into the flower, would depress the labellum and would be less likely to disturb the rostellum, until it had sucked the nectar and began to retreat. When a dead bee, with the four waxy balls of pollen dangling by their caudicles from its back, is forced into another flower, some or all of them are caught with certainty by the broad, shallow, and highly viscid stigmatic surface, which likewise tears off the grains of pollen from the threads of the caudicles.

That living humble-bees can thus remove the pollinia is certain. Sir W. C. Trevelyan sent to Mr. Smith of the British Museum a Bombus hortorum, which was forwarded to me—caught in his hothouse, where a Cattleya was in flower—with its whole back, between the wings, smeared with dried viscid matter, and with the four pollinia attached to it by their caudicles, ready to be caught by the stigma of any other flower if the bee had entered one.