Page:Darwin - The various contrivances by which orchids are fertilized by insects (1877).djvu/261

. VIII. of Malaxis paludosa, the close resemblance between the two membranes of the clinandrum and the fertile anther, in shape, texture, and in the height to which the spiral vessels extended, was most striking: it was impossible to doubt that in these two membranes we had two rudimentary anthers. In Evelyna, one of the Epidendreæ, the clinandrum was similarly formed, as were the horns of the clinandrum in Masdevallia, which serve in addition to keep the labellum at the proper distance from the column. In Liparis pendula and some other species, these two rudimentary anthers form not only the clinandrum, but likewise wings, which project on each side of the entrance into the stigmatic cavity, and serve as guides for the insertion of the pollen-masses. In Acropera and Stanhopea, as far as I could make out, the membranous borders of the column, down to its base, were also thus formed; but in other cases, as in Cattleya, the wing-like borders of the column seem to be simple developments of the two pistils. In this latter genus, as well as in Catasetum, these same two rudimentary stamens, judging from the position of the vessels, serve chiefly to strengthen the back of the column; and the strengthening of the front of the column is the sole function of the third stamen of the inner whorl (a$3$), in those cases in which it was observed. This third stamen runs up the middle of the column to the lower edge, or lip, of the stigmatic cavity.

I have said that in the Ophreæ and Neotteæ the spiral vessels of the inner whorl, marked a$1$, a$2$, a$3$ in the diagram, are entirely absent, and I looked carefully for them; but in nearly all the members of these two tribes, two small papillæ, or auricles as they have been often called, stand in exactly the position which the two first of these three anthers would have occupied,