Page:On the Various Contrivances by Which British and Foreign Orchids are Fertilised by Insects, and on the Good Effects of Intercrossing.djvu/25



The drum-like pedicel is of the highest importance, not only by rendering the viscid disc more prominent and more likely to stick to the face of an insect whilst inserting its proboscis into the nectary beneath the stigma, but on account of its power of contraction. The pollinia lie inclined backwards in their cells (see Fig. A), above and some way on each side of the stigmatic surface; if attached in this position to the head of an insect, the insect might visit any number of flowers, and no pollen could be left on the stigma. But observe what takes place: in a few seconds after the inner end of the drum-like pedicel is removed from its embedded position and exposed to the air, one side of the drum contracts, and this contraction draws the thick end of the pollinium inwards, so that the caudicle and the viscid surface of the disc are no longer parallel, as they were at first, and as they are presented in the section C. At the same time the drum rotates through nearly a quarter of a circle, and this moves the caudicle downwards, like the hand of a clock, depressing the thick end of the pollinium or mass of pollen-grains. After this double movement, the right-hand disc, for instance, being supposed to be affixed to the right side of an insect's face, when the insect, after a short interval of time, visits another flower, the pollen-bearing end of the pollinium will have moved downwards and inwards, and will now infallibly strike the viscid surface of the stigma, situated in the middle beneath and between the two anther-cells.

The little rudimentary tail of the caudicle projecting beyond the drum-like pedicel is an interesting point to those who believe in the modification of species; for it shows us that the disc has moved a little inwards, and that primordially the two discs stood even still further in advance of the stigma than they do at present. It shows us that the parent-form approached a little more closely in structure to that extraordinary Orchid the Bonatea speciosa of the Cape of Good Hope.