Although in no true Orchid, excepting Cypripedium, the two anthers (a 1 and a2) of the inner whorl are fully developed, their rudiments are generally present and are often utilised; for they generally form the membranous sides of the clinandrum, or cup 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 of Malaxis paludosa, the close resemblance between the membranes of the clinandrum and the fertile anther, in shape, texture, and in the height to which the spiral vessels extend, is most striking: it is impossible to doubt that in these two membranes we see two rudimentary anthers. In Evelyna, one of the Epidendreæ, the clinandrum was similarly formed, as were the horns of the clinandrum in Masdevallia, which likewise serve to keep the labellum at the proper distance from the column. In Liparis pendula and some other forms, these two rudimentary anthers formed not only the clinandrum, but likewise wings, projecting on each side of the entrance to the stigmatic cavity, and serving 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 seemed 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, served 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 (a3) of the inner whorl, in those cases in which I observed it. 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 Ophrea and Neottee the spiral vessels, marked al, a2, a3 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 exact the position which the two first of these three anthers would have occupied, had they been developed. Not only do they stand in this position, but the column in some cases, as in Cephalanthera, has on each side a prominent ridge, running from them to the bases or mid-ribs of the two upper petals; that is, in the proper position of the filaments of these two stamens. It is, again, impossible to doubt that the membranes of the clinandrum in Malaxis are formed by these two anthers in a rudimentary and modified condition. Now, from the perfect clinandrum of Malaxis, through that of Spiranthes, Goodyera, Epipactis latifolia, and E. palustris (see Fig. XIV. and XIII.), to the minute and slightly flattened auricles in the genus Orchis, a perfect gradation can be traced. Hence I conclude that these auricles are doubly rudimentary; that is, that they are rudiments of the membranous sides of the clinandrum, these membranes themselves being rudiments of the two anthers so often referred to. The absence of spiral vessels running to the auricles by no means seems sufficient to overthrow these several arguments on their much-disputed nature; that such vessels may quite disappear, we have proof in Cephalanthera grandiflora, in which the rostellum and its vessels are completely aborted.
Finally, then, with respect to the six stamens or anthers which ought to be represented in every Orchid: the three belonging to the outer whorl are always present, with the upper one generally fertile, and the two lower ones invariably petalold and forming part of the labellum; the three stamens of the inner whorl are less plainly developed, especially the lower one, a3, which, when it can be detected, serves only to strengthen the column, and, in some rare cases, according to Brown, forms a separate projection, or filament; the upper two anthers of this inner whorl are fertile 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 Orchids, 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 on the foregoing views, namely in Habenaria, and in the allied 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; the vessels running into their mid-ribs and into all the other more important organs persue the same identical course as in all the other Ophreæ. The vessels on the sides of the upper sepal, instead of uniting with the mid-rib, and entering the posterior ovarian group, diverge and enter the postero-lateral groups: again, the vessels on the anterior side of the upper petals, instead of uniting with the mid-rib and entering the postero-lateral ovarian groups, diverge, or wander from their proper course, and enter the antero-lateral groups.
