Page:Darwin - The various contrivances by which orchids are fertilized by insects (1877).djvu/67

. II. as the viscid matter quickly sets hard when exposed to the air. The pouch is not elastic, and does not spring up when the pollinium is removed. Such elasticity would have been useless, as there is here a separate pouch for each viscid disc; whereas in Orchis, after one pollinium has been removed, the other has to be kept covered up and ready for action. Hence it appears that nature had been so economical as to save even superfluous elasticity.

The polinnia cannot, as I have often proved, be shaken out of the anther-cells. That insects of some kind visit the flowers, though not frequently, and remove the pollinia, is certain, as we shall immediately see. Twice I have found abundant pollen on the stigmas of flowers, in which both polinnia were still in their cells; and no doubt this might have been much oftener observed. The elongated labellum affords a good landing-place for insects: at its base, just beneath the stigma, there is a rather deep depression, representing the nectary in Orchis; but I could never see a trace of nectar within it; nor have I ever observed any insects approach these inconspicuous and scentless flowers, often as I have watched them. There is, however, on each side of the base of the labellum a small shining projection, having an almost metallic lustre, which appears curiously like a drop of fluid or nectar; and as these flowers are only visited occasionally by insects, Sprengel's view of the existence of sham-nectaries is far more probable in this case than in any other known to me. On several occasions I have detected minute punctures in these protuberances, but I was not able to decide whether they had been made by insects, or whether superficial cells had spontaneously burst. Similar shining protuberances are present on the labella of all the other species of Ophrys. The two rostella stand not far