Page:Darwin - The various contrivances by which orchids are fertilized by insects (1877).djvu/35

. I. flowers almost always have both pollinia removed, whilst the younger flowers close beneath the buds, which will have been seldomer visited, have frequently only one pollinium removed. In a spike of Orchis maculata, I found as many as ten flowers, chiefly the upper ones, which had only one pollinium removed; the other pollinium being still in its proper place with the lip of the rostellum well closed up; so that all the mechanism was perfect for its subsequent removal by some other insect.

When the first edition of this book was published, I had not seen any insects visiting the flowers of the present species; but a friend watched some plants, and saw them visited by several humble-bees, apparently Bombus muscorum; and Dr. H. Müller has seen four other species of Bombus at work. He caught ninety-seven specimens, and of these thirty-two had pollinia attached to their heads.

The description now given of the action of the organs in Orchis mascula applies to O. morio, fusca, maculata, and latifolia. These species present slight and apparently co-ordinated differences in the length of their caudicles, in the direction of the nectary, in the shape and position of the stigma, but they are not worth detailing. In all, the pollinia when removed from the anther-cells undergo the curious movement of depression, which is so necessary to place them in a right position on an insect's head for striking the stigmatic surface of another flower. Six species of humble-bees, the hive-bee and two other kinds have been seen by H. Müller and myself visiting the flowers of Orchis morio. On some of the