Page:Darwin - The various contrivances by which orchids are fertilized by insects (1877).djvu/257

. VIII. labellum; and seven run up the great central column. These vessels are arranged, as may be seen, in rays proceeding from the axis of the flower; and all on the same ray invariably run into the same ovarian group; thus the vessels supplying the upper sepal, the fertile anther (A$1$), and the upper pistil or stigma (i. e. the rostellum S$r$), all unite and form the posterior ovarian group. Again, the vessels supplying, for instance, the left lower sepals, the corner of the labellum and one of the two stigmas (S) on the same side, unite and form the antero-lateral group; and so with all the other vessels.

Hence, if the existence of groups of spiral vessels can be trusted, the flower of an Orchid certainly consists of fifteen organs, in a much modified and confluent condition. We see three stigmas, with the two lower ones generally confluent, and with the upper one modified into the rostellum. We see six stamens, arranged in two whorls, with generally one alone (A$1$) fertile. In Cypripedium, however, two stamens of the inner whorl (a$1$ and a$2$) are fertile, and in other Orchids these two are represented more plainly in various ways than the remaining stamens. The third stamen of the inner whorl (a$3$), when its vessels can be traced, forms the front of the column: Brown thought that it often formed a medial excrescence, or ridge, cohering to the labellum; or, in the case of Glossodia, a filamentous organ, freely projecting in front of the labellum. The former conclusion does not agree with my dissections; about Glossodia I know nothing. The two infertile stamens of the outer whorl (A$2$, A$3$) were believed by Brown to be only occasionally represented, and then by lateral excre-