THE FEMALE FLOWER IN CYCADEiE AND CONIFERS. 453 



On the Structure of the Female Floioer in CYCADEiE 

 and ConiferjB. 



That the apex of the nucleus is the point of the ovukim 

 where impregnation takes place, is at least highly probable, 

 both from the constancy in the appearance of the embryo 

 at that point, and from the very general inversion of the 

 nucleus ; for by this inversion its apex is brought nearly, 

 or absolutely, into contact with that part of the parietes of 

 the ovarium, by which the influence of the pollen may be 

 supposed to be communicated. In several of those families 

 of plants, however, in which the nucleus is not inverted, 

 and the placentae are polyspermous, as Cistinese,-^ it is diffi- 

 cult to comprehend in what manner this influence can pss 

 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. 



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 

 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 struc- 

 ture of Cycadese, of Coniferse, 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 



' This structure of ovulum, indicated by lliat of the seed, as characterising 

 and defining the limits of Cistineaj (namely, Oistus, Helianthemum, Hudsonia, 

 and Lechea), I communicated to Dr. Hooker, by whom it is noticed in his 

 Flora ScoHcco (p. 284), published in 1821 ; where, however, an observation is 

 added respecting Gajrtner's description of Cistus and Heliauthemum, for which 

 I am not accountable. 



