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

150 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

.



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

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-