Page:Darwin - The various contrivances by which orchids are fertilized by insects (1877).djvu/258

238 scences on the labellum; but I find the corresponding vessels invariably present in the labellum of every Orchid examined,—even when the labellum is very narrow or quite simple, as in Malaxis, Herminium, or Habenaria.

We thus see that an Orchid-flower consists of five simple parts, namely, three sepals and two petals; and of two compounded parts, mamely, the column and labellum. The column is formed of three pistils, and generally of four stamens, all completely confluent. The labellum is formed of one petal with two petaloid stamens of the outer whorl, likewise completely confluent. I may remark, as making this fact more probable, that in the allied Marantaceæ the stamens, even the fertile stamens, are often petaloid, and partially cohere. This view of the nature of the labellum explains its large size, its frequently tripartite form, and especially the manner of its coherence to the column, unlike that of the other petals. As rudimentary organs vary much, we can thus perhaps understand the variability, which as Dr. Hooker informs me is characteristic of the excrescences on the labellum. In some Orchids which have a spur-like nectary, the two sides are apparently formed by the two modified stamens; thus in Gymnadenia conopsea (but not in Orchis pyramidalis), the vessels, proceeding from the two antero-lateral ovarian groups, run down the sides of the nectary; those from the single anterior group run down the exact middle of the nectary, then returning up the opposite side form the mid-rib of the labellum. The sides of the nectary being thus formed of two distinct organs, apparently explains the tendency,