the rostellum of the stigma of violets, or of the operculum of many mosses

1922, John Christopher Willis, "Orchidacea", entry in A Manual and Dictionary of the Flowering Plants and Ferns, page 471,
The rostellum has an outer firm pouch, inside which is the viscid substance to which are firmly attached the caudicles of the pollinia. An insect entering the fl. probes the spur of the labellum and its back comes into contact with the rostellum and depresses the pouch, causing the viscid substance to adhere to the insect.

In many orchids there is a discrete "viscidium," or sticky pad, formed by the rostellum.

2005, Orchids of Manitoba: A Field Guide, Native Orchid Conservation Inc., page 20,
The third stigma is sterile and has developed into the rostellum, a sticky structure that aids in pollination by attaching the pollen to insects.

The morphology of the scolex, particularly the rostellum, is also useful in diagnosis; T. saginata has no rostellum and its scolex bears no hooks, making it easily distinguishable from T. solium, which has an armed rostellum.

The scolex exhibits a retractable rostellum with crowns of recurved thorn-like hooks and four cup-like suckers.

Some species also possess an anteriorly projecting rostellum, which may or may not be armed with one or more rows of hooks. The rostellum can be retracted into the rostellar sac within the scolex.

Rostellum

Meaning

Noun

Rhymes