660 



of tlie luicleus it is terminated by a splierical mass consisting of globular cells. The 

 primary utricle at this period assumes the character of the suspensor (Mirbel), and its 

 spherical extremity constitutes the first trace of the embryo. 



" In \he fifth period, the apex of the nucleus and of its integument becomes more 

 inclined towards the placenta ; the spherical extremity of the suspensor enlarges, and 

 it becomes more evident that it constitutes the rudimental embryo. In the mean time 

 the suspensor has become lengthened by an increase in the number of its cells ; and 

 its upper extremity is found to be protruded through the apex of the embryo-sac, the 

 apex of the nucleus and the micropyle. From this extremity there is a considerable 

 development of cells, many of which hang loosely in the passage leading to the con- 

 ducting tissue of the style, while the rest unite in forming a process which passes 

 down the outer side of the ovulum within the carpellary cavity. This process is com- 

 posed of from nine to twelve rows of cells, and its extremity resembles in appearance 

 and in the anatomical condition of its cells the spongiole of a root. By a slight trac- 

 tion of this cellular process, the suspensor with the embryo may be withdrawn from the 

 embryo-sac through the exostome, thus proving the continuity of the process with the 

 suspensor, and through it with the embryo itself. 



" During the sixth period the suspensor becomes more attenuated ; and the cellular 

 process has reached the base of the ovulum, the cells of its extremity abounding with 

 cytoblasts, which prove that it is still progressing in development. The embryo also 

 increases in size, and two lateral processes are observed, which evidently fonn the 

 first traces of the cotyledons. 



" In the seventh period, all distinction between the nucleus and its integument 

 ceases, and they form a single envelope enclosing the embryo-sac ; the cellular pro- 

 cess has become so much developed, that its extremity has passed round the base of 

 the ovulum and is directed towards the placenta ; and the lateral processes of the em- 

 bryo have become distinct fleshy cotyledons, enclosing both the radicle and plumule 

 in corresponding depressions of their opposed surfaces. The subsequent changes 

 consist chiefly in the great development of the cotyledons, which ultimately occupy 

 the entire cavity of the nucleus, filling the space usually taken up by albumen. 

 " From these observations Dr. Giraud deduces the following inferences. 

 " The formation of the embryo-sac, and the development of cytoblasts within it, 

 having been shown to take place at a period prior to impregnation, and even the pri- 

 mary utricle itself making its appearance before the emission of the pollen from the 

 anther, and before the expansion of the stigma, the origin of the primary utricle can- 

 not be referred to the influence of impregnation, nor can it have been derived from 

 the pollen tube pressing before it a fold of the embryo-sac. 



" The primary utricle at its first formation being quite distinct from the embryo- 

 sac, even at its apex (although brought into contact with it at a subsequent period, 

 and ultimately penetrating it), cannot result from a depression or involution of the 

 embryo-sac, as is maintained by M. Brongniart. 



" The pollen tubes (which after impregnation may be traced in the conducting 

 tissue of the style) never reaching the micropyle, but pollen granules being found in 

 abundance in the channel leading to it, and being doubtless brought into contact with 

 the outer surface of the embryo-sac through the exostome ; and the first trace of the 

 embryo appearing at this time in the formation of the spherical body at the inferior 

 extremity of the primary utricle — Dr. Giraud is led to conclude that the origin of this 

 simple spherical body results from a peculiar process of nutrition, determined by the 



