Page:Darwin - The various contrivances by which orchids are fertilized by insects (1877).djvu/289

. IX. curious square viscid disc to become securely cemented to an insect's head or body.

As in Epipactis the cup at the base of the labellum serves as a nectar-receptacle, I expected to find that the analogous cups in Stanhopea, Acropera, &c., would serve for the same purpose; but I could never find a drop of nectar in them. According, also, to M. Ménière and Mr. Scott this is never the case in these genera, or in Gongora, Cirrhæa, and many others. In Catasetum tridentatum, and in the female form Monachanthus, we see that the upturned cup cannot possibly serve as a nectar-receptacle. What then attracts insects to these flowers? That they must be attracted is certain; more especially in the case of Catasetum, in which the sexes stand on separate plants. In many genera of Vandeæ there is no trace of any nectar-secreting organ or receptacle; but in all these cases (as far as I have seen), the labellum is either thick and fleshy, or is furnished with extraordinary excrescences, as in the genera Oncidium and Odontoglossum. In Phalænopsis grandiflora there is a curious anvil-shaped projection on the labellum, with two tendril-like prolongations from its extremity which turn backwards and apparently serve to guard the sides of the anvil, so that insects would be forced to alight on its crown. Even in our British Cephalanthera grandiflora, the labellum of which never contains nectar, there are orange-coloured ribs and papillæ on the inner surface which faces the column. In Calanthe (fig. 26) a cluster of odd little spherical warts projects from the labellum, and there is an extremely long nectary, which does not include nectar; in Eulophia viridis the short nectary is equally destitute of nectar, and the labellum