Dr. Giraud's Contributions to f^egetable Embryology. 167 



trochet, and name it the hypostate, as pointing out merely its anatomical 

 relations. 



The cellular process proceeding from the extremity of the suspensor, next 

 the exostome, around the outer surface of the ovule into the carpellary cavity, 

 is an organ of somewhat unusual occurrence ; but from its mode of growth 

 and structural relations, it may be inferred to be of very essential importance 

 to the origin and development of the embryo. Now it has been recently 

 pointed out by F. G. F. Meyen*, that in the great majority of instances the pol- 

 len-tube, after having penetrated the micropyle, is brought in contact with the 

 apex of the embryo-sac, with which it there contracts an adhesion : from this 

 period the changes consequent on impregnation date their commencement ; 

 and, under the direct influence of this immediate application of the fovilla to 

 the embryo-sac, continue with uninterrupted regularity. But in the case of 

 Tropceolum majus, as the pollen-tube never reaches the embryo-sac, some ad- 

 ditional means are required to insure that influence of the fovilla on the pri- 

 mary utricle which is necessary for the development, at its extremity, of the 

 spherical cellular body, which subsequently becomes the embryo. This action, 

 then, is effected by the projection of this cellular process from the primary 

 utricle, which, by being immersed (so to speak) in the fovilla, is made the 

 medium for the transmission of the latter to the primary utricle, and through 

 it to the embryo itself; for which office the structure of its extremity (so like 

 a spongiole) renders it peculiarly fitted. 



It may now be shown how far the foregoing observations bear upon the 

 undetermined question of the origin of the embryo. That in this plant the 

 primary utricle and the future embryo never have any structural connexion 

 with the extremity of the pollen-tube at their first origin, or at any subsequent 

 period of their development, is sufficiently obvious from the fact, that the 

 pollen-tube is never brought into contact with the embryo-sac. As the 

 primary utricle makes its appearance before impregnation has occurred, it 

 cannot be possible that that organ has ever formed the extremity of the pol- 

 len-tube, as is believed to be the case by Schleiden and Wydler. Moreover, 

 as the primary utricle takes its origin wholly within the embryo-sac, and at 

 the earliest period of its formation is not in contact with that membrane, it 

 * F. G. F. Meyen, ' Neues System der Pflanzen-Physiologie. 



