Page:Darwin - The various contrivances by which orchids are fertilized by insects (1877).djvu/204

184 membrane, to which the pedicel is united, with an inferior cushion of great thickness, of pulpy, flocculent, and viscid matter. The posterior margin is much the most viscid part, and this necessarily first strikes any object when the pollinium is ejected. The viscid matter soon sets hard. The whole surface of the disc is kept damp before ejection, by resting close against the roof of the stigmatic chamber; but in the section (fig. C) it is represented, like the other parts, a little separated from the roof.

The connective membrane of the anther (a in all the figures) is produced into a spike, which adheres loosely to the pointed end of the column; this pointed end (f, fig. C) is homologically the filament of the anther.

The anther has this peculiar shape apparently for the sake of leverage, so that it may be easily torn off by a pull at its lower end, when the pollinium is jerked out by the elasticity of the pedicel.

The labellum stands at right angles to the column, or hangs a little downwards; its lateral and basal lobes are turned under the middle portion, so that an insect can stand only in front of the column. In the middle of the labellum there is a deep cavity, bordered by crests. This cavity does not secrete nectar, but its walls are thick and fleshy, with a slightly sweet nutritious taste; and it will presently be shown that they are gnawed by insects. The extremity of the left-hand antenna stands immediately over the cavity, and would infallibyinfallibly [sic] be touched by an insect visiting this part of the labellum for any purpose.

The antennæ are the most singular organs of the flower, and occur in no other genus. They form rigid, curved horns, tapering to a point. They consist of a narrow ribbon of membrane, with the edges curled inwards so as to touch; each horn therefore is tubular,