Page:Darwin - The various contrivances by which orchids are fertilized by insects (1877).djvu/84

64 beneath the two pouches. Now let us suppose an insect to alight on one side of the labellum so as first to lick up the exposed drop of nectar on this side; from the position of the pouch exactly over the drop, it would almost certainly get the pollinium of this side attached to its head. If it were now to go to the mouth of the true nectary, the pollinium attached to its head from not having as yet become depressed would not touch the stigma; that there would be no self-fertilisation. The insect would then probably suck the exposed drop of nectar on the other side of the labellum, and would perhaps get another pollinium attached to its head; it would thus be considerably delayed by having to visit the three nectaries. It would then visit other flowers on the same plant, and afterwards flowers on a distinct plant; and by this time, but not before, the pollinia will have undergone the movement of depression and will be in a proper position for effecting cross-fertilisation. It thus appears that the secretion of nectar at three separate points of the labellum,—the wide distance apart of the two rostella,—and the slow downward movement of the caudicle without any lateral movement—are all correlated for the same purpose of cross-fertilisation.

To what extent this Orchis is frequented by insects, and what the kinds are, I do not know, but several of the flowers on two spikes, sent me by the Rev. B. S. Maiden, had a single pollinium removed, and one flower had both removed.

We now come to two genera, namely, Gymnadenia and Habenaria or Platanthera, including four British species, which have uncovered viscid discs. The viscid matter, as before remarked, is of a somewhat different nature from that in Orchis, Ophrys, &c., and does not