168 Dr. Giraud's Contributions to Fegetable Embryology. 



cannot have been formed by the pollen-tube pressing before it a fold of the 

 embryo-sac in its passage into the cavity of that structure, as Schleiden has 

 maintained. 



The researches of F. G. F. Meyen* sufficiently prove that the present is not 

 a solitary exception to the mode of origin of the embryo, which Schleiden and 

 Wydler have described ; for that observer has shown, from a very extended 

 series of researches, that in those instances in which the pollen-tube reaches 

 the embryo-sac, it never penetrates, nor in any way enters the cavity of that 

 structure ; but that, after it has contracted an adhesion with the outer surface 

 of the embryo-sac, the primary utricle {vesicule embryonnaire, F. G. F. Meyen) 

 takes its origin within that cavity, so that the lining membrane of the embryo- 

 sac always intervenes between the primary utricle and the extremity of the 

 pollen-tube. It is evident that Schleiden and Wydler have been misled by 

 not properly distinguishing this fact, nor being sufficiently careful to observe 

 the relations of the primary utricle at its very first appearance. The point at 

 which these observers believe the pollen-tube to lose its connexion with the 

 primary utricle, is in fact its true extremity, which never has had any organic 

 union with that body. The intimate nature of the impregnation of those 

 plants in which the pollen-tube is brought in contact with the embryo-sac, is 

 essentially the same as that of Tropasolum majus ; but, in the latter, the fovilla 

 is applied to the embryo-sac independently of the application of the pollen- 

 tube to its outer surface ; and its influence on the development of the embryo 

 is sustained through the medium of the cellular process extending from the 

 suspensor or true umbilical cord. The direction of the axis of the embryo 

 (being opposed to that of the nucleus and its membrane) is such as would be 

 anticipated from the fact of its commencing its development at the apex of 

 the embryo-sac ; therefore the views which we may entertain of the morphology 

 of the ovule do not necessarily afford an argument in favour of the doctrines 

 of Schleiden and Wydler, nor in any other way affect the question of the mode 

 of origin of the embryo. 



I have noticed in the preceding observations, that the first appearance of 

 the cotyledons is accompanied by a corresponding elongation of the axis of 

 the embryo, owing to an extension of its globular cells, so that the cotyledons 



* F. G. F. Meyen. Opus cit. 



