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
respect