Page:Darwin - The various contrivances by which orchids are fertilized by insects (1877).djvu/157

. V. the flowers in the hothouse at Kew, for many eggs were deposited within it, near the base.

Of Bolbophyllum I examined the curious little flowers of four species, which I will not attempt fully to describe. In B. cupreum and coccinum, the upper and lower surfaces of the rostellum resolve themselves into viscid matter, which has to be forced upwards by insects into the anther, so as to secure the pollinia. I effected this easily by passing a needle down the flower, which is rendered tubular by the position of the labellum, and then withdrawing it. In B. rhizophoræ the anther-case moves backwards, when the flower is mature, leaving the two pollen-masses fully exposed, adhering to the upper surface of the rostellum. They are held together by viscid matter, and, judging from the action of a bristle, are always removed together. The stigmatic chamber is very deep with an oval orifice, which exactly fits one of the two pollen-masses. After the flower has remained open for some time, the sides of the oval orifice close in and shut the stigmatic chamber completely,—a fact which I have observed in no other Orchid, and which, I presume, is here related to the much exposed condition of the whole flower. When the two pollinia were attached to a needle or bristle, and were forced against the stigmatic chamber, one of the two glided into the small orifice more readily than could have been anticipated. Nevertheless, it is evident that insects must place themselves on successive visits to the flowers in precisely the same position, so as first to remove the two pollinia, and then force one of them into the stigmatic orifice. The two upper filiform petals would serve as guides to the insect; but the labellum, instead of making the flower tubular, hangs down just like a tongue out of a widely open mouth.