Page:Darwin - The various contrivances by which orchids are fertilized by insects (1877).djvu/90

70 anther-cells are separated from each, other by a wide space of connective membrane, and the pollinia are enclosed in a backward sloping position (fig. 11). The viscid discs front each other, and stand in advance of the stigmatic surface. In consequence of their forward position, the caudicles and pollen-masses are much elongated. Each viscid disc is circular, and, in the early bud, consists of a mass of cells, of which the exterior layers (answering to the lip or pouch in Orchis) resolve themselves into adhesive matter. This matter has the property of remaining adhesive for at least twenty-four hours after the pollinium has been removed from its cell. The disc, externally covered with a thick layer of adhesive matter (see fig. C, which stands so that the layer of viscid matter is below) is produced on its opposite and embedded side into a short drum-like pedicel. This pedicel is continuous with the membranous portion of the disc and is formed of the same tissue. The caudicle of the pollinium is attached in a transverse direction to the embedded end of the pedicel, and its extremity is prolonged, as a bent rudimentary tail, just beyond the drum. The caudicle is thus united to the viscid disc in a very different manner, and in a plane at right angles, to what occurs in the other British Orchids. In the short drum-like pedicel, we have a small development of the long pedicel of the rostellum, which is so conspicuous in many Vandeæ, and which connects the viscid disc with the true caudicles of the pollinia.

The drum-like pedicel is of the highest importance, not only by rendering the viscid disc more prominent and more likely to stick to the face of an insect whilst inserting its proboscis into the nectary beneath the stigma, but on account of its power of contraction. The pollinia lie inclined backwards in their cells (see