My attention having been directed by the Rev. Professor Henslow, to a remarkable irritability of the rostellum in a common English orchideous plant, the Listera ovata, I have taken the earliest opportunity of following up his observations on the living plant, and of dissecting the organ in question; an account of the anatomy and functions of which I have now the honour of laying before the Royal Society. The rostellum of Listera ovata is a broad, blunt, tongue-shaped organ, terminating the column, and projecting forwards, below the anther, and above the stigma. Soon after the flower opens, if the rostellum be touched or irritated, two white viscid masses are instantaneously protruded,—one from each side of the apex ; these coalesce and form a considerable gland-like body, which attaches itself at once to the bases of the pollen-masses, and usually continues firmly to adhere to the apex of the rostellum also.