Page:On the Various Contrivances by Which British and Foreign Orchids are Fertilised by Insects, and on the Good Effects of Intercrossing.djvu/19

 position exactly adapted to strike the stigmatic surface, which is situated, relatively to the pouch-formed rostellums, rather lower down in the flower than in the Fly Ophrys. If we compare the woodcut of the pollinium of the present species, or Spider Ophrys, after the movement, with that of the Fly Ophrys, which is incapable of movement, it is impossible to doubt that the permanent rectangular bend near the disc of the latter serves the same end as the movement of depression.

I examined fourteen flowers of the Spider Ophrys, several of which were partly withered; both pollinia were removed in none, and in three alone one pollinium had been removed. Hence this species, like the Fly Ophrys, apparently is not much visited by insects.

The anther-cells are remarkably open, so that, in travelling in a box, two pair of pollinia had fallen out, and were sticking by their viscid discs to the flower. Here we have, as throughout nature, evidence of gradation; for though the wide opening of the anther-cells is of no use to this species, it is of the highest importance, as we shall immediately see, to the following species, namely, the Bee Ophrys. So, again, the flexure of the upper end of the caudicle of the pollinium towards the labellum, though of service to the Spider and Fly Ophrys, in order that the pollinium, when removed by insects and carried to another flower, should strike the stigma, is exaggerated in the following species, and serves for the very different purpose of self-fertilisation.

Ophrys apifera. In the Bee Ophrys we meet with widely different means of fertilisation as compared with the other species of the genus, and, indeed, as far as I know, with all other Orchids. The two pouch-formed rostellums, the viscid discs, and the position of the stigma, are nearly the same as in other species of Ophrys; but to my surprise, I have observed that the distance of the two pouches from each other, and the shape of the mass of pollen-grains, are variable. The caudicles of the pollinia are remarkably long, thin, and flexible, instead of being, as in all the other Ophrea, rigid enough to stand upright. They are necessarily curved forward at their upper ends, owing to the shape of the anther-cells; and the pear-shaped masses of pollen lie embedded high above and directly over the stigma. The anther-cells naturally open soon after the flower is fully expanded, and the thick ends of the pollinia fall out, the viscid discs still remaining in their pouches. Slight as is the weight of the pollen, yet the caudicle is so thin, and soon becomes so flexible, that, in the course of a few hours, they sink down, until they hang freely in the air (see lower pollen-mass in Fig. A) exactly opposite to and in front of the stigmatic surface. When in this position a breath of air, acting on the expanded petals, sets the flexible and elastic caudicles vibrating, and they almost immediately strike the viscid stigma, and, being there secured, impregnation is effected. To make sure that no other aid was requisite, though the experiment was