Rostellum

Definition and stakes

Portrait of Charles Darwin Charles Darwin,  The Various Contrivances by which Orchids are Fertilised by Insects (1877)

“ The anterior face of the rostellum (r, C, D) projects a little beyond the surface of the upper part of the stigma, and this is of importance. In the early bud the rostellum consists of a friable mass of cells, with the exterior surface rough: these superficial cells undergo a great change during development, and become converted into a soft, smooth, highly elastic membrane or tissue, so excessively tender that it can be penetrated by a human hair; when thus penetrated, or when slightly rubbed, the surface becomes milky and in some degree viscid, so that the pollen-grains adhere to it. ”
Source: Wikisource

Portrait of Charles Darwin Charles Darwin,  The Various Contrivances by which Orchids are Fertilised by Insects (1877)

“ In order to compare the minute structure of the rostellum and stigma, I examined young flower-buds of Epidendrum cochleatum and floribundum, which, when mature, have a simple rostellum. The posterior parts of both organs were quite similar. The whole of the rostellum at this early age consisted of a mass of nearly orbicular cells, containing spheres of brown matter, which resolve themselves into the viscid fluid. The stigma was covered with a thinner layer of similar cells, and beneath them were the coherent spindle-formed utriculi. ”
Source: Wikisource

Portrait of Charles Darwin Charles Darwin,  The Various Contrivances by which Orchids are Fertilised by Insects (1877)

“ The thin and elongated rostellum of Acropera projects at right angles to the column (see diagram, fig. 23, p. 150) ; and the pedicel of the pollinium is of course equally long and much thinner. The disc consists of an extremely small cap, viscid within, which fits on the extremity of the rostellum. The viscid matter sets hard but slowly. The upper sepal forms a hood enclosing and protecting the column. The labellum is an extraordinary organ, baffling all description: it is articulated to the column by a thin strap, so elastic and flexible that a breath of wind sets it vibrating. ”
Source: Wikisource

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