In several of those families of plants, however, in which the nucleus is not inverted, and the placentae are polyspermous, as Cistineae,* it is difficult to comprehend in what manner this influence can reach its apex externally, except on the supposition, not hastily to be admitted, of an impregnating aura filling the cavity of the ovarium; or by the complete separation of the fecundating tubes from the placentae, which, however, in such cases I have never been able to detect.
(*Footnote.

This structure of ovulum, indicated by that of the seed, as characterizing and defining the limits of Cistineae (namely, Cistus, Helianthemum, Hudsonia and Lechea) I communicated to Dr.Hooker, by whom it is noticed in his Flora Scotica (page 284) published in 1821; where, however, an observation is added respecting Gaertner's description of Cistus and Helianthemum, for which I am not accountable.) It would entirely remove the doubts that may exist respecting the point of impregnation, if cases could be produced where the ovarium was either altogether wanting, or so imperfectly formed, that the ovulum itself became directly exposed to the action of the pollen, or its fovilla; its apex, as well as the orifice of its immediate covering, being modified and developed to adapt them to this economy.
But such, I believe, is the real explanation of the structure of Cycadeae, of Coniferae, of Ephedra, and even of Gnetum, of which Thoa of Aublet is a species.
To this view the most formidable objection would be removed, were it admitted, in conformity with the preceding observations, that the apex of the nucleus, or supposed point of impregnation, has no organic connexion with the parietes of the ovarium.

In support of it, also, as far as regards the direct action of the pollen on the ovulum, numerous instances of analogous economy in the animal kingdom may be adduced.
The similarity of the female flower in Cycadeae and Coniferae to the ovulum of other phaenogamous plants, as I have described it, is indeed sufficiently obvious to render the opinion here advanced not altogether improbable.

But the proof of its correctness must chiefly rest on a resemblance, in every essential point, being established, between the inner body in the supposed female flower in these tribes, and the nucleus of the ovulum in ordinary structures; not only in the early stage, but also in the whole series of changes consequent to fecundation.

Now as far as I have yet examined, there is nearly a complete agreement in all these respects.