Page:On the Various Contrivances by Which British and Foreign Orchids are Fertilised by Insects, and on the Good Effects of Intercrossing.djvu/49

The last genus of the Malaxeæ which I will mention is Dendrobium, of which one at least of the species, namely D. chrysanthum, is interesting, from being apparently contrived to affects its own fertilisation, if an insect, when visiting the flower, should accidentally fail to remove the pollen masses. The rostellum has an upper and a small lower surface composed of membrane; and between these a thick mass of milky-white matter is included, which can be very easily forced out. This white matter is less viscid than usual; when exposed to the air a film forms over it in less than half a minute, and it soon sets into a waxy or cheesy substance. Beneath the rostellum the large concave but shallow viscid stigmatic surface is seated. The produced anterior lip of the anther (see A) almost entirely covers the upper surface of the rostellum. The filament of the anther is of considerable length, but is hidden in the sideview, A, behind the middle of the anther; in the section, B, it is seen, after it has sprung forward: it is elastic, and presses the anther firmly down on the inclined surface of the clinandrum (see section B) which lies behind the rostellum. When the flower is expanded the two pollinia, united into a single mass, lie quite loose on the clinandrum and under the anther-case. The labellum embraces the column, leaving a tubular passage in its front; the middle portion (as may be seen in its section, in Fig. A) is thickened; the thickened portion extends up as far as the top of the stigma. The lowest part of the labellum is developed into a saucer-like nectary, which secretes honey.

If an insect forced its way into one of these flowers, the labellum, which is elastic, would yield, and the projecting lip of the anther would protect the rostellum from being disturbed; but when the insect retreats, the lip of the anther will be lifted up, and the viscid matter from the rostellum will be forced into the anther, gluing the pollen-mass to the insect, which will thus transport it to another flower. I easily imitated this action; but as the pollen-masses have no caudicle, and lie rather far back within the clinandrum under the