Page:Darwin - The various contrivances by which orchids are fertilized by insects (1877).djvu/166

146 Those species which I have examined of Lælia, Leptotes, Sophronitis, Barkeria, Phaius, Evelyna, Bletia, Chysis, and Cœlogyne, resemble Cattleya in the caudicles of the pollinia being free, and in the viscid matter from the rostellum not coming into contact with them without mechanical aid, as well as in their general manner of fertilisation. In Cœlogyne cristata the upper lip of the rostellum is much elongated. In Evelyna carivata and Chysis eight balls of waxy pollen are all united to a single caudicle. In Barkeria the labellum, instead of enfolding the column, is pressed against it, and this would effectually compel insects to brush against the rostellum. In Epidendrum we have a slight difference; for the upper surface of the rostellum, instead of permanently remaining membranous, as in the above-named genera, is so tender that by a touch it breaks up, together with the whole lower surface, into a mass of viscid matter. In this case the whole of the rostellum, together with the adherent pollinia, must be removed by insects as they retreat from the flower. I observed in E. glaucum that viscid matter exuded from the upper surface of the rostellum when touched, as happens with Epipactis. In fact it is difficult to say, in these cases, whether the upper surface of the rostellum should be called membrane or viscid matter. With Chysis this matter sets nearly hard and dry in twenty minutes, and quite so in thirty minutes after its removal from the rostellum.

In Epidendrum floribundum there is a rather greater difference: the anterior horns of the clinandrum (i. e. the cup on the summit of the column in which the pollinia lie) approach each other so closely as to adhere to the two sides of the rostellum, which consequently lies in a nick, with the pollinia seated over