Page:Darwin - The various contrivances by which orchids are fertilized by insects (1877).djvu/170

presented in the diagram) protrude in a not fully-hardened condition through a small slit, and adhere to the back of the rostellum. The upper surface of the rostellum is generally hollowed out for the reception of the pollen-masses; it is represented as smooth in the diagram, but is really often furnished with crests

Fig. 23.

Imaginary Section, illustrative of the structure of the column in the Vandeæ.

(1.) The filament, bearing the anther with its pollen-masses; the anther is represented after it has opened along its whole under surface, so that the section shows only the dorsal surface.

(2.) The upper pistil, with the upper part modified into the rostellum.

(3.) The two lower confluent pistils, bearing the two confluent stigmas.

or knobs for the attachment of the two caudicles. The anther afterwards opens more widely along its under surface, and leaves the two pollen-masses unattached, excepting by their caudicles to the rostellum.

During an early period of growth, a remarkable change has been going on in the rostellum: either its extremity or its lower surface becomes excessively viscid (forming the viscid disc), and a line of separa-