140 CONTRIBUTIONS TO VEGETABLE EMBRYOLOGY. 



nucleus it is terminated by a spherical mass consisting of globular cells. 

 The primary utricle at this period assumes the character of the suspen- 

 sor (Mirbel), and its spherical extremity constitutes the first trace of 

 the embryo. 



In the fifth period the apex of the nucleus and of its integument be- 

 comes 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 ex- 

 tremity 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 conducting 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 composed 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 traction of this cellular process the suspensor with the em- 

 bryo may be withdrawn from the embryo- sac through the exostome, 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 pro- 

 gressing in development. The embryo also increases in size, and two 

 lateral processes are observed, which evidently form the first traces of 

 the cotyledons. 



In the seventh period all distinction between the nucleus and its in- 

 tegument ceases, and they form a single envelope enclosing the embryo- 

 sac ; the cellular process has become so much developed, that its ex- 

 tremity has passed round the base of the ovulum and is directed 

 towards the placenta; and the lateral processes of the embryo have 

 become distinct fleshy cotyledons, enclosing both the radicle and plu- 

 mule 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 impreg- 

 nation, and even the primary utricle itself making its appearance before 



