Page:Darwin - The various contrivances by which orchids are fertilized by insects (1877).djvu/205

. VII. with a slit down one side, like an adder's fang. They are composed of numerous, much elongated, generally hexagonal cells, pointed at both ends; and these cells (like those in most of the other tissues of the flower) have nuclei with nucleoli. The antennæ are prolongations of the sides of the anterior face of the rostellum. As the viscid disc is continuous with a little fringe of membrane on each side, and as this fringe is continuous with the bases of the antennæ, these latter organs are put into direct connection with the disc. The pedicel of the pollinium passes, as already stated, between the bases of the two antennæ. The antennæ are not free for their whole length; but their exterior edges are firmly united to and blend for a considerable space with the margins of the stigmatic chamber.

In all the flowers which I examined, taken from three plants, the two antennæ which are alike in structure occupied the same relative position. The extreme part of the left-hand antenna bends upwards (see B, fig. 28, in which the position is shown plainer than in A), and at the same time a little inwards, so that its tip is medial and guards the entrance into the cavity of the labellum. The right-hand antenna hangs down, with its tip turned a little outwards; and as we shall immediately see, is almost paralysed, so as to be functionless.

Now for the action of the parts. When the left-hand antenna of this species (or either of the antennæ in three of the following species) is touched, the edges of the upper membrane of the disc, which are continuously united with the surrounding surface, instantly rupture, and the disc is set free. The highly elastic pedicel then instantly flirts the heavy disc out of the stigmatic chamber with such force, that the whole pollinium is ejected, bringing away with it the two