Page:On the Various Contrivances by Which British and Foreign Orchids are Fertilised by Insects, and on the Good Effects of Intercrossing.djvu/17

 Fig. V.

a. anther. rr. rostellum. s. stigma. l. labellum.

First for the genus Ophrys.

In Ophrys muscifera, or the Fly Ophrys, the chief peculiarity is that the caudicle of the pollinium (B) is doubly and almost rectangularly bent. The nearly circular piece of membrane, to the under side of which the ball of viscid matter is attached, is of considerable size, and plainly forms the summit of the rostellum, instead of forming, as in Orchis, the posterior and upper surface; consequently the attached end of the caudicle, after the flower has expanded, is exposed to the air. As might have been expected from this circumstance, the caudicle is not capable of that movement of depression, characteristic of all the species of Orchis; for this movement is always excited when the upper membrane of the disc is first exposed to the air. The ball of viscid matter is bathed with fluid within the pouch formed by the lower half of the rostellum, and this is necessary, as the viscid matter rapidly sets hard in the air. The pouch is not elastic, and does not spring up when the pollinium is removed. Such elasticity would have been of no use, 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 would appear as if nature were so economical as to save even superfluous elasticity.

The pollinia cannot, as I have often tried, be jarred out of the anther-cells by violence. That insects of some kind visit these 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 their own pollinia were still in their cells; and, no doubt, had I oftener looked, I should have oftener observed this fact. The elongated labellum affords a good standing-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; nor have I observed any insects, often as I have watched these inconspicuous and scentless flowers, even approach them. On each side of the base of the labellum there is a shining knob, with an almost metallic lustre, appearing like two drops of fluid; and if I could in any case believe in Sprengel's sham-nectaries, I should believe it in this instance. What induces insects to visit these flowers I can at present only conjecture. The two pointed pouches, covering the viscid discs, stand not far apart, and project over the stigma: any object gently pushed right against one of them (in Orchis the push should be directed rather downwards) depresses the pouch, touches and adheres to the viscid ball, and the pollinium is easily removed.