Page:On the Various Contrivances by Which British and Foreign Orchids are Fertilised by Insects, and on the Good Effects of Intercrossing.djvu/69



The flower presents an extraordinary appearance, and its mechanism is more curious even than its appearance (Fig. XXIX.). The base of the column is bent baclwards, at right angles to the ovarium or footstalk, and then resumes an upright position to near its summit, where it is again bent. It is, also, twisted in a unique manner, so that its front surface, including the anther, rostellum, and the upper part of the stigma, faces laterally to either the right or left hand in the flowers on the opposite sides of the spike. The twisted stigmatic surface, in an equally peculiar manner, extends down to the base of the column: at its upper end it forms a deep cavity, beneath the protuberant rostellum (pd in the drawing), in which the large viscid disc of the pollinium is lodged.

The anther-case (a in the drawing) is elongated and triangular, closely resembling that of Catasetum: it does not extend up to the apex of the column. This apex consists of a thin flattened filament, which in the bud is straight, but before the flower expands becomes much more bent by the pressure of the labellum. A group of spiral vessels runs up the column as far as the summit of the anther-case; they are then reflexed and run some way down the anther-case. The point of reflexion forms a short thread-like hinge by which the notched top of the anther-case is articulated to the column close beneath its bent summit. The hinge, although less than a pin's head in size, is of paramount importance, for it is sensitive and conveys the stimulus from a touch to the disc of the pollinium: it serves also as a guide in the act of ejection. As it conveys the necessary stimulus to the disc, one may suspect that part of the tissue of the rostellum, which lies in close contact with the filament of the anther, runs up to this point; but I could detect no difference in structure in comparison with the same parts in Catasetum. The cellular tissue round the hinge is gorged with fluid, for a large drop exudes when the