Page:Darwin - The various contrivances by which orchids are fertilized by insects (1877).djvu/233

. VII. down, but the two upper petals remain nearly upright. The bases of the sepals, and especially of the two upper petals, are thick and swollen and have a yellowish tint; when quite mature, they are so gorged with fluid, that, if punctured by a fine glass tube, the fluid rises by capillary attraction to some height in it. These swollen bases, as well as the footstalk of the labellum, have a decidedly sweet and pleasant taste; and I can hardly doubt that they are attractive to insects, for no free nectar is secreted.

I will now endeavour to show how all the parts of the flower are co-ordinated and act together. The pedicel of the pollinium is bowed round the rostellum, as in Catasetum; in this latter genus, when freed, it merely straightens itself with force, in Mormodes something more takes place. If the reader will look forward to fig. 34 (p. 223), he will see a section of the flower-bud of the allied genus of Cycnoches, which differs only in the shape of the anther and in the viscid disc having a much deeper dependent curtain. Now let him suppose the pedicel of the pollinium to be so elastic that, when freed, it not only straightens itself, but suddenly bends back on itself with a reversed curvature, so as to form an irregular hoop. The curved surface which was before in contact with the protuberant rostellum now forms the outside of the hoop. The exterior surface of the curtain, which depends beneath the disc, is not viscid; and it now lies on the anther-case, with the viscid surface of the disc on the outside. This is exactly what takes place with Mormodes. But the pollinium assumes with such force its reversed curvature (aided, apparently, by a transverse curling outwards of the margins of the pedicel), that it not only forms itself into a hoop, but suddenly springs away from the protuberant