Page:Darwin - The various contrivances by which orchids are fertilized by insects (1877).djvu/264

244 some doubt on the view that the labellum is always an organ compounded of one petal and two petaloid stamens; for if any one were to assume that from some unknown cause the lateral vessels of the lower petals had diverged in an early progenitor of the Orchidean order from their proper course into the antero-lateral ovarian groups, and that this structure had been inherited by all existing Orchids, even by those with the smallest and simplest labellums, I could answer only as follows; but the answer is, I think, satisfactory. From the analogy of other monocotyledonous plants, we might expect the hidden presence of fifteen organs in the flowers of the Orchideæ, arranged alternately in five whorls; and in these flowers we find fifteen groups of vessels exactly thus arranged. Hence there is a strong probability that the vessels, A$2$ and A$3$, which enter the sides of the labellum, not in one or two cases, but in all the Orchids seen by me, and which occupy the precise position which they would have occupied had they supplied two normal stamens, do really represent modified and petaloid stamens, and are not lateral vessels of the labellum which have wandered from their proper course. In Habenaria and Bonatea, on the other hand, the vessels proceeding