Page:Darwin - The various contrivances by which orchids are fertilized by insects (1877).djvu/260

240 all were observed excepting a$3$, which is the most difficult one to trace, and apparently is oftenest absent. In the Cypripedeæ, again, all were traced except a$3$, which, I feel pretty sure, was here really absent: in this tribe the stamen (A$1$) is represented by a conspicuous shield-like rudiment, and a$1$ and a$2$ are developed into two fertile anthers. In the Ophreæ and Neotteæ all were traced, with the important exception of the vessels belonging to the three stamens (a$1$, a$2$, and a$3$) of the inner whorl. In Cephalanthera grandiflora, I clearly saw a$3$ proceeding from the anterior ovarian group, and running up the front of the column. This anomalous Orchid has no rostellum, and the vessel marked S$r$ in the diagram was entirely absent, though seen in every other species.

Although the two anthers (a$1$ and a$2$) of the inner whorl are not fully and normally developed in any Orchid, excepting Cypripedium, their rudiments are generally present and are often utilised; for they often form the membranous sides of the cup-like clinandrum on the summit of the column, which includes and protects the pollen-masses. These rudiments thus aid their fertile brother-anther. In the young flower-bud