Page:Darwin - The various contrivances by which orchids are fertilized by insects (1877).djvu/263

. VIII. in Cypripedium, and in other cases are generally represented either by membranous expansions, or by minute auricles without spiral vessels. These auricles, however, are sometimes quite absent, as in some species of Ophrys.

On this view of the homologies of Orchid-flowers, we can understand the existence of the conspicuous central column,—the large size, generally tripartite form, and peculiar manner of attachment of the labellum,—the origin of the clinandrum,—the relative position of the single fertile anther in most of the genera, and of the two fertile anthers in Cypripedium,—the position of the rostellum, as well as of all the other organs,—and lastly, the frequent occurrence of a bilobed stigma, and the occasional occurrence of two distinct stigmas. I have encountered only one case of difficulty, namely in Habenaria and the allied genus, Bonatea. These flowers have undergone such an extraordinary amount of distortion, owing to the wide separation of their anther-cells and of the two viscid discs of the rostellum, that any anomaly in them is the less surprising. The anomaly relates only to the vessels supplying the sides of the upper sepal and of the two upper petals; for the vessels running into their midribs and into all the other more important organs pursue the same identical course as in the other Ophreæ. The vessels which supply the sides of the upper sepal, instead of uniting with the midrib and entering the posterior ovarian group, diverge and enter the postero-lateral groups. Again, the vessels on the anterior side of the two upper petals, instead of uniting with those of the midrib and entering the postero-lateral ovarian groups, diverge, or wander from their proper course, and enter the antero-lateral groups.

This anomaly is so far of importance, as it throws