Page:Darwin - The various contrivances by which orchids are fertilized by insects (1877).djvu/198

CHAPTER VII.

VANDEÆ continued.—CATASETIDÆ.

Catasetidæ, the most remarkable of all Orchids—The mechanism by which the pollinia of Catasetum are ejected to a distance and are transported by insects—Sensitiveness of the horns of the rostellum—Extraordinary difference in the male, female, and hermaphrodite forms of Catasetum tridentatum—Mormodes ignea, curious structure of the flowers; ejection of the pollinia—Mormodes luxata—Cycnoches ventricosum, manner of fertilisation.

I have reserved for separate description one sub-family of the Vandeæ, namely, the Catasetidæ, which must, I think, be considered as the most remarkable of all Orchids.

I will begin with Catasetum. A brief inspection of the flower shows that here, as with most other Orchids, some mechanical aid is requisite to remove the pollen-masses from their cells, and to carry them to the stigmatic surface. We shall, moreover, presently see that Catasetum is exclusively a male form; so that the pollen-masses must be transported to the female plant, in order that seed should be produced. The pollinium is furnished with a viscid disc of huge size; but this, instead of being placed in a position likely to touch and adhere to an insect visiting the flower, is turned inwards and lies close to the upper and back surface of a chamber, which must be called the stigmatic chamber, though functionless as a stigma. There is nothing in this chamber to attract insects; and even if they did enter it, the viscid surface of the disc could not possibly come into contact with them.