Botany.] 
NATURAf. HISTORY. 
555 
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 fecun- 
dating tubes from the placentae, which, however, in such 
cases I have never been able to detect. 
It would entirely remove the doubts that may exist re- 
specting the point of impregnation, if cases could be pro- 
duced where the ovarium was either altogether wanting, or 
so imperfectly formed, that the ovulum itself became di- 
rectly 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 struc- 
ture 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 re- 
gards the direct action of the pollen on the ovulum, nu- 
merous instances of analogous economy in the animal king- 
dom may be adduced. 
The similarity of the female flower in Cycadeae. and Coni- 
feree 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 
Helianthemum, Hudsonia and Lechea), I communicated to Dr. 
Hooker, by whom it is noticed in his Flora Scotica, (p. 284,) pub- 
lished in 1821 ; where, however, an observation is added respecting 
Gsertner’s description of Cistus and Helianthemum, for which I am 
not accountable. 
