142 GENERATION. 



nucleus a little membranous sac, (that is to say a 

 utricle) which he considers as the first sketch (ebauche) 

 of the embryo. This is not in opposition with what I 

 have seen and published. But he affirms, that this sac 

 is no other than the extremity of the tube and this is 

 what is to be doubted ; according to this philosopher, 

 the doctrine of the existence of sexes in plants is 

 erroneous. The analogy which has been supposed to 

 exist with animals is untenable. To the stamen alone 

 belongs the generative power ; the pistil only serves the 

 purpose of gestation. M. Spach and I hope, however, 

 to prove, that in certain species, the utricle which is sup- 

 posed to commence the embryo already exists at an epoch 

 when the pistil is enveloped in such a manner that the 

 tube of the pollen can find no practicable way to arrive 

 at it." Brongniart recals to mind, " that in his memoir 

 upon the generation of plants, he has proved, that in 

 some plants, and particularly in the Cucurbitacese, the 

 embryo vesicle looked upon by Schleiden, as formed 

 by the extremity of the pollen-tubes, existed before 

 fecundation had taken place. Since when, he is farther 

 assured of the extension of the tubes of pollen to the 

 summit of the nucleus, and of their adherence with 

 this part of the ovule in a great number of plants ; but 

 that it appears very doubtful to him, that the extremities 

 of these tubes are the origins of embryos, as M. Schlei- 

 den and Wydler pretend." 



246. In connection with this it is best perhaps 

 to mention the recent discoveries of Mr. Griffiths, 

 who has proved the remarkable fact of the ovule in 

 Loranthus and Viscum not being formed till some 

 time after the diffusion of pollen on the stigma. The 

 results of his observations, which only can be given, 

 are that 



a. During an early period the ovary is solid. 



b. That the ovule is formed posterior to fecundation, 

 and that it manifests itself in a cavity formed by an ex- 

 cavation of the tissue of the ovary. 



c. That the first development of the embryo appears 



