Page:Darwin - The various contrivances by which orchids are fertilized by insects (1877).djvu/45

. I. fly to another plant, and thus effect a union between two distinct individuals.

Orchis ustulata resembles O. pyramidalis in some important respects, and differs from it in others. The labellum is deeply channelled, and the channel which replaces the guiding ridges of O. pyramidalis leads to the small triangular orifice of the short nectary. The upper angle of the triangle is overhung by the rostellum, the pouch of which is rather pointed below. In accordance with this position of the rostellum, close to the mouth of the nectary, the stigma is double and lateral. This species shows in an interesting manner how easily two distinct stigmas, like those of O. pyramidalis, might be converted into a single one, by becoming at first slightly lobed like that of O. mascula, and then acquiring its present structure. For directly beneath the rostellum there is a narrow transverse rim, formed of true stigmatic tissue, which connects together the two lateral stigmas; so that if this rim were widened, the two stigmas would be converted into a single transverse one. Conversely a single stigma might thus easily be converted into a double one. The pollinia undergo the usual movement of depression, and in acquiring this position the two diverge slightly, so as to be ready to strike the two lateral stigmas.

Orchis (sub-genus Himantoglossum) hircina.—A fine specimen of this extremely rare British plant, the Lizard Orchis, with its curious elongated labellum, was sent me by Mr. Oxenden. The two pollinia arise from a single almost square disc; and when