Page:Darwin - The various contrivances by which orchids are fertilized by insects (1877).djvu/97

. II. together. As in Platanthera flava, there is a process at the base of the labellum which compels moths to enter the flower on either side. The nectary, according to Mr. Trimen and Mr. J. Mansel Weale, does not contain free nectar; but the latter author believes that the tissue of which it is composed tastes sweet, so that moths probably penetrate it for the sake of the intercellular fluid. The pollinia are of astonishing length, and when removed from their cases hang down merely from the weight of the pollen-masses, and if attached to the head of an insect would be in a proper position for adhering to the stigma. Mr. Weale has likewise described some other South African species of Bonatea. These differ from B. speciosa in having their nectaries full of nectar. He found a small butterfly, Pyrgus elmo, "perfectly embarrassed by the number of pollinia of this Bonatea attached to its sternum." But he does not specify whether the sternum was naked or covered with scales.

The South African genera Disa and Disperis are placed by Lindley in two sub-tribes of the Ophreæ. The superb flowers of Disa grandiflora have been described and figured by Mr. Trimen. The posterior sepal, instead of the labellum, is developed into a large nectary. In order that insects may reach the copiously stored nectar, they must insert their proboscides on either side of the column; and in accordance with this fact the viscid discs are turned outwards in an extraordinary manner. The pollinia are crooked, and when removed bend downwards from their own weight, so that no movement is necessary for placing themselves in a proper position. Considering the large supply of