Osyris, Loranthus and Viscum. \W 



M. Schleiden assumes the applicability of his conclusions, drawn from 

 direct observation in several plants, to all others in which direct observa- 

 tion is more difficult, on three distinct grounds ; the first of which, regarding 

 the diameter of the tube outside the sac and just within it, is, I cannot but 

 think, of very minor importance, neither does it present itself in Santalum: 

 the second, which would confine certain peculiar contents to the pollen tube, 

 appears to me contradicted by Santalum and Loranthns; and the third, which 

 positively refers plurality of embryos to a plurality of pollen tubes, is contra- 

 dicted in a most marked manner by Loranthus. 



I am unacquainted with any other observations on this most interesting 

 point, except those of M. Mirbel, which were, in France, I have reason to 

 believe, considered to carry a signal refutation of the views of M. Schleiden. 

 but which certainly have not convinced me; and I cannot help imbibing the 

 belief that the primordial utricle of M. Mirbel and M. Spach is the sac of the 

 embryo, which no doubt often, and perhaps generally, exists before fecun- 

 dation. 



M. Mirbel has thus summed up the conclusions arrived at by M. Schleiden 

 regarding the relations of the boyau and the sac of the embryo ; and I quote 

 it to show, that he has put on it a construction similar to that which I have 

 previously ventured to do : — " Quand la cavite ovoide s'est accrue et en meme 

 temps le sac embryonnaire qui la tapisse, le boyau issu des grains du pollen 

 penetre jusqu'au sommet du nucelle, pousse en avant la paroi du sac embry- 

 onnaire, qui gfede a sa pression, et forme un caecum dans lequel il loge son 

 extremite anterieure. 



" La partie du boyau pollinique logee dans le caecum se renfle en massue 

 et produit, dans sa cavite, un tissu utriculaire qui la remplit et se moule sur 

 elle ; tandis que la partie posterieure de ce meme boyau reste en dehors sous 

 sa forme primitive de tube membraneux. Cette partie ne tardera pas a dis- 

 paraitre ; l'autre, metamorphosee en embryon, commencera une nouvelle gene- 

 ration*." 



To that which regards the inflection of the sac of the embryo before the 

 pollen tube I at least attach considerable importance, because it appears to me 

 to weaken if possible the great merit of M. Schleiden's observations, and to 

 * Comptes Rendus, No. 12, March 25, 1839. 



