( 685 ) XXXV. On the Organs and Mode of Fecundation in Orchidea and Asclepiadece. By Robert Brown, Esq., V.P.L.S., <^c. Read November 1 and 15, 1831. In the Essay now submitted to the Society, my principal object is to give an account of some observations, made chiefly in the course of the present year, on the structure and economy of the sexual organs in Orchideae and Asclepiadeae, — the two families of phaenogamous plants which have hitherto presented the most important objections to the prevailing theories of vegetable fecundation. But before entering on this account, it is necessary to notice the various opinions that have been held respecting the mode of impregnation in both families : and in concluding the sub-ject of Orchideae, I shall advert to a few other points of struc-ture in that natural order. ORCHIDE^. The authors whose opinions or conjectures on the mode of impregnation in Orchideae I have to notice, may be divided into such as have considered the direct application of the pollen to the stigma as necessary : and those who, — from cer-tain peculiarities in the structure and relative position of the sexual organs in this family, — have regarded the direct contact of these parts as in many cases difficult or altogether impro-bable.