164 Dr. Giraud's Contributions to Vegetable Embryology. 



extend into the carpellary cavity ; but the fovilla, with its granules, is found 

 abundantly in the passage leading from the style to the exostome (fig. 4, i.) *. 

 With the increased development of the embryo-sac, the primary utricle, as it 

 elongates, becomes distinctly cellular, by the development of minute cells in 

 its interior, while at the extremity, next the base of the nucleus, it is termi- 

 nated by a spherical extremity, consisting of numerous globular cells (k.). 

 The primary utricle, at this period, assumes the character of the suspensor 

 (Mirbel); and its spherical extremity constitutes the first trace of the em- 

 bryo. 



Fifth Period. — At this stage the apex of the nucleus, with that of its tegu- 

 mentary membrane, becomes directed more towards the axis of the pistil. The 

 spherical extremity of the suspensor enlarges, and almost entirely fills the 

 cavity of the embryo-sac ; and it now becomes more evident that it consti- 

 tutes the axis of the embryo (fig. 5, k.). The suspensor {h.) is, in a correspond- 

 ing degree, lengthened by an increase in the number and size of its cells ; 

 while its upper extremity has now protruded through the apex of the embryo- 

 sac, the apex of the nucleus, and through 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 others 

 unite in forming a process which passes round the outside of the ovule into 

 the carpellary cavity, and between the inner surface of the carpel and the 

 outer surface of the ovule {m.). This process of cellular tissue is composed 

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

 and in the anatomical condition of its cells, the spongiole of a root. When 

 the ovule is removed from its carpel, and slight traction is made upon this 

 cellular process, the suspensor, with the embryo, may be withdrawn from the 

 embryo-sac, through the exostome and apex of the nucleus (fig. 6.) ; thus 

 proving the perfect continuity of this cellular process with the suspensor, and 

 through it with the embryo itself. 



Sixth Period. — The suspensor is now more attenuated, consisting only, as 



* Many other instances might be adduced in which the pollen tubes have not been found to pene- 

 trate so far as the micropyle. L. C. Treviranus mentions that there are whole families of plants in 

 which be baa never been able to discover any pollen tubes at all ; and F. G. F. Meyen has never been 

 able to trace themin Urtica urens. 



