Page:Darwin - The various contrivances by which orchids are fertilized by insects (1877).djvu/81

. II. odour. They seem highly attractive to insects; in a spike with only seven flowers recently open, four had both pollinia, and one had a single pollinium removed.

When the first edition of this book appeared I did not know how the flowers were fertilised, but my son George has made out the whole process, which is extremely curious and differs from that in any other Orchid known to me. He saw various minute insects entering the flowers, and brought home no less than twenty-seven specimens with pollinia (generally with only one, but sometimes with two) attached to them. These insects consisted of minute Hymenoptera (of which Tetrastichus diaphantus was the commonest), of Diptera and Coleoptera, the latter being Malthodes brevicollis. The one indispensable point appears to be that the insect should be of very small size, the largest being only the $1⁄20$ of an inch in length. The pollinia were always attached to the same place, namely, to the outer surface of the femur of one of the front legs, and generally to the projection formed by the articulation of the femur with the coxa. The cause of this peculiar mode of attachment is sufficiently clear: the middle part of the labellum stands so close to the anther and stigma, that insects always enter the flower at one corner, between the edge of the labellum and one of the upper petals; they also almost always crawl in with their backs turned directly Or obliquely towards the labellum. My son saw several which began to crawl into the flowers in a different position; but they came out and changed their position. Standing in either corner of the flower, with their backs turned towards the labellum, they insert their heads and fore legs into the short nectary, which is seated between the two widely separated viscid discs. I ascertained that they had occupied this position by