Osyris, Loranthus and Viscum. 207 



has not been shown ; that the identity of the vesicle with the uppermost less 

 cellular part of the whole mass of the embryo has not been ascertained ; and 

 further, that the frequent appearance of this as having on separation an entire 

 margin, is an objection to its having been derived from the pollen tube. 



To put beyond doubt these objections, and many others that will of course 

 generally suggest themselves, would exceed my ability. I am satisfied if the 

 results are considered to be not altogether unreasonably arrived at, and if 

 they are found to agree with the aggregate results of others' experience. 



In no instance has the structural investigation of any particular plant been 

 pushed so far as to leave nothing to be desired by the observer, or to be ob- 

 served by others. Actual observation of all the minuter points of structure is 

 scarcely to be expected in any plant, for the advantages it may present in 

 some respects will probably be counterbalanced by disadvantages affecting 

 others ; so that our knowledge of structure is more derived from numerous 

 incomplete, than from a few complete observations. 



Although few plants can be supposed to present such facilities for observing 

 the circumstances attending the establishment of direct relations between the 

 embryonary sac and the end of the pollen tube, the opacity and, so to say, 

 the callosity of the apex of that sac present positive disadvantages. And the 

 subsequent cellularity of the sac reduces again the facility of determining the 

 identity of the original vesicle, and the upper less cellular parts of the embryo- 

 nic mass. 



From such experience as I have been able to collect, I have derived a con- 

 viction that, whenever filaments, such as pollen tubes are known to be, are found 

 in the canal of the style only after obvious action of the pollen upon the stig- 

 matic surface, and that these are traceable downwards directly into the ovula, 

 it is legitimately assumable that those filaments are pollen tubes ; and I pro- 

 ceed on this assumption to observe the consequences, as if I had actually 

 ascertained the continuity of the filament with the inner membrane of the 

 pollen grain. 



With regard to the identity of the vesicle with the uppermost less cellular 

 part of the mass of the embryo, I believe that few persons would have exa- 

 mined a numerous series of fecundated ovula without coming to the conclusion 

 which I have ventured to advance ; it occupies the situation that the vesicle 



