Page:Darwin - The various contrivances by which orchids are fertilized by insects (1877).djvu/137

. IV. it is divided by longitudinal septa into a series of loculi, which contain viscid matter and have the power of violently expelling it. These loculi show traces of their original cellular structure. I have met with this structure in no other genus except in 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. When the flower is fully expanded, the pollinia are left quite free, supported behind by the anther-cells, and lying in front against the concave back of the rostellum, with their upper 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 broken off easily. After the flower has long remained open, the pollen becomes more friable. The labellum is much elongated, contracted at its base, and bent downwards, as represented in the drawing; the upper half above the bifurcation is furrowed along the middle; and the borders of this furrow secrete much nectar.

As soon as the flower opens, if the crest of the rostellum be touched ever so lightly, a large drop of viscid fluid is instantaneously expelled; and this, as Dr. Hooker has shown, is formed by the coalescence of two drops proceeding from two depressed spaces on each side of the centre. A good proof of this fact was afforded by some specimens kept in weak spirits of wine, which apparently had expelled the viscid matter slowly, and here two separate little spherical balls of hardened matter had been formed, attached to the two pollinia. The fluid is at first slightly opaque and milky; but on exposure to the air for less than a second, a film forms over it, and in two or three