Page:Darwin - The various contrivances by which orchids are fertilized by insects (1877).djvu/24

 form together the column. Ordinary stamens consist of a filament, or supporting thread (rarely seen in British Orchids), which carries the anther; and within the anther lies the pollen or male vivifying element. The anther is divided into two cells, which are very distinct in most Orchids, so much so as to appear in some species like two separate anthers. The pollen in all common plants consists of fine granular powder: but in most Orchids the grains cohere in masses, which are often supported by a very curious appendage, called the caudicle. This part and all the other organs will, hereafter be more fully described and figured under the head of the first species, Orchis mascula. The pollen-masses, with their caudicles and other appendages, are called the pollinia.

Orchids properly have three pistils or female organs, united together, the upper and anterior surfaces of two of which form the two stigmas. But the two are often completely confluent, so as to appear as one. The stigma is penetrated in the act of fertilisation by long tubes, emitted by the pollen-grains, which carry the contents of the grains down to the ovules or young seeds in the ovarium.

The upper stigma is modified into an extraordinary organ, called the rostellum, which in many Orchids presents no resemblance to a true stigma. When mature it either includes or is altogether formed of viscid matter. In many species the pollen-masses are firmly attached to a portion of the exterior membrane, which, when insects visit the flowers, is removed, together with the pollen-masses. This removable portion consists in most British Orchids merely of a small piece of membrane, with a layer or ball of viscid matter underneath, and I shall call it the "viscid disc;" but in many exotic species the portion removed is so