Page:Darwin - The various contrivances by which orchids are fertilized by insects (1877).djvu/92

72 flowers, and the strong sweet odour emitted by them at night, all show that this plant depends for its fertilisation on the larger nocturnal Lepidoptera. I have often found spikes with almost all the pollinia removed. From the lateral position and distance of the two viscid discs from each other, the same moth would generally remove only one pollinium at a time; and in a spike which had not as yet been much visited, three flowers had both pollinia, and eight flowers had only one pollinium removed. From the position of the discs it might have been anticipated that they would adhere to the side of the head or face of moths; and Mr. F. Bond sent me a specimen of Hadena dentina with one eye covered and blinded by a disc, and a specimen of Plusia v. aureum with a disc attached to the edge of the eye. Mr. Marshall collected twenty specimens of Cucullia umbratica on an island in Derwentwater, separated by half-a-mile of water from any spot where H. chlorantha grew; nevertheless, seven of these moths had the pollinia of this Orchid affixed to their eyes. Although the discs are so adhesive that almost all the pollinia in a bunch of flowers which was carried in my hand and thus shaken were removed by adhering to the petals or sepals, yet it is certain that moths, probably the smaller species, often visit these flowers without removing the pollinia; for on examining the discs of a large number of pollinia whilst still in their cells I found minute Lepidopterous scales glued to them.

The cause of the flowers of various kinds of Orchids being constructed so that the pollinia are always affixed to the eyes or proboscides of Lepidoptera, and to the naked foreheads or proboscides of Hymenoptera,