Page:On the Various Contrivances by Which British and Foreign Orchids are Fertilised by Insects, and on the Good Effects of Intercrossing.djvu/40

 one of the two pairs. I noticed one flower with all its four pollinia in place, with a single pollen-leaf within the stigmatic cavity; and this must clearly have been brought by some insect. I found pollen-leaves on the stigmas of many other flowers. The plant produces plenty of seed: on one spike, thirteen of the twenty-one lower flowers had formed large capsules.

Listera ovata, or Tway-blade

The structure and action of the rostellum of this Orchid has been the subject of a highly remarkable paper in the Philosophical Transactions, by Dr. Hooker, who has described minutely, and of course correctly, its curious structure; he did not, however, attend to the part which insects play in the fertilisation of this flower. C. K. Sprengel well knew the importance of insect-agency, but he misunderstood both the structure and the action of the rostellum. The rostellum is of large size, thin, or foliaceous; convex in front and concave behind, with its sharp summit slightly hollowed out on each side; it arches over the stigmatic surface (Fig. XVIII. r. s. A). Internally, according to Dr. Hooker, it is divided by longitudinal septa into a series of loculi, which contain and subsequently expel with violence viscid matter. These loculi show traces of their original cellular structure. I have met with this structure of the rostellum in no other genus excepting the closely allied Neottia. The anther, situated behind the rostellum, and protected by a broad expansion of the top of the column, opens in the bud. The pollinia, when the flower is fully expanded, are left quite free, supported behind by the anther-cells, and lying in front against the concave back of the rostellum, with their upper and pointed ends resting on its crest. Each pollinium is almost divided into two masses. The pollen-grains are attached together in the usual manner by a few elastic threads; but the threads are weak, and large masses of pollen can be easily broken off. After the flower has long remained open, the pollen becomes more friable. The labellum is much elongated, contracted at the base, and bent downwards, as represented in the drawing; it is furrowed along the middle, from its bifurcation close up to the base of the stigma; and the borders of the furrow are glandular and secrete much nectar.