THE PHYTOLOGIST. 



No. XXXIII. 



FEBRUARY, MDCCCXLIV. 



Price Is. 



Art. CXCIV. — Researches in Emhryogeny. By W. Wilson, Esq. 

 (Continued from p. 73.5). 



The introversion of the embryo-sac, although insisted upon as an 

 established fact, is still not an essential part of the theory of Schlei- 

 den. It is possible that the apex of the sac might have a minute aper- 

 ture immediately below the micropyle ; or the pollen-tube might, by 

 perforating the membrane, gain admission to the interior, instead of 

 propelling the upper half of the sac, as it is stated to do, into the lower 

 half of the membrane to form a double wrapper for the nascent em- 

 bryo. And although it is considered that sufficient proof has been 

 obtained that no such introversion takes place, and that thus the en- 

 tire theory, so far as it rests on the authority of Schleiden, is consider- 

 ably weakened if not altogether set aside ; it is not so easy to dispose 

 of the question whether or not the pollen-tube enters the micropyle : 

 to deny it would be to contravene the statements of some of the most 

 able physiologists of the time, while the most diligent investigations 

 of my own have failed to supply the smallest reason for adopting 

 their views. 



Wydler says : — " On doit a M. R. Brown la connaissance de la 

 route que suit le boyau pollinique depuis le stigmate, — j usque dans 

 I'ovule meme, en y entrant par son micropyle ; mais c'est la que s'ar- 

 reterent les observations de I'illustre Anglais, Cette route indiquee 

 par lui, fut constatee par les recherches de M, Brongniart fils, corarae 

 par celles de M. Corda."* It also appears that even Mirbel and 

 Spach entertain a similar opinion. For my own part, I have not suc- 

 ceeded in tracing the pollen-tubes very much below the stigma ; and 

 perhaps the pains bestowed in this method of investigation might 

 have well been spared, because in most cases the micropyle is so si- 

 tuated with respect to the placenta, that a void space must be traversed 

 by the pollen-tube in its progress thither; or at least the pollen-tube 

 must glide along the surface of the ovule after leaving the placenta, 

 before it can enter the micropyle ; and thus, without any very minute 



* Annales cles Sciences Nat. tome xi. p. 144. 



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