Page:Darwin - The various contrivances by which orchids are fertilized by insects (1877).djvu/46

26 they are removed from their cells, they do not diverge, but become depressed, sweeping through an angle of ninety degrees, in about thirty seconds. They are then in a proper position for striking the single large stigma which lies beneath the rostellum. In the case of O. pyramidalis we have seen that the depression of the two pollinia is effected by the contraction of the disc in front of each, two furrows or valleys being there formed; whilst with the present species, the whole front of the disc contracts or sinks down, the front part being thus separated from the hinder part by an abrupt step.

Aceras (Orchis) anthropophora.—The caudicles of the pollinia are unusually short; the nectary consists of two minute rounded depressions in the labellum; the stigma is transversely elongated; and lastly the two viscid discs lie so close together within the rostellum that they affect each other's outline. This latter fact is worth notice, as a step towards the two becoming absolutely confluent, as in the following species of Aceras, in O. pyramidalis and hircina. Nevertheless, in Aceras a single pollinium is sometimes removed by insects, though more rarely than with the other species of Orchis.

Aceras (Orchis) longibracteata.—Mr. Moggridge has given an interesting account, together with a figure, of this plant which grows in the South of France. The pollinia are attached to a single viscid disc. When they are removed they do not diverge as in O. pyramidalis, but converge and then undergo the