228 DR. GIRAUD EMBRYOLOGY [BOOK n. 



there is formed an elongated diaphanous utricle (primary 

 utricle ; ' utricule primordiale/ Mirbel ; ' vesicule embryon- 

 naire/ F. G. F. Meyen ; ' 1'extremite anterieure du boyan 

 pollinique/ Schleiden) containing a quantity of globular 

 matter (' globulocellular cambium/ Mirbel ; ( cytoblasts/ 

 Schleiden). This primary utricle is developed wholly within 

 the embryo-sac, from which it can be clearly seen to be 

 distinct. 



Fourth Period (after impregnation has occurred). The 

 pollen tubes do not extend into the carpellary cavity ; but the 

 fo villa, with its granules, is found abundantly in the passage 

 leading from the style to the exostome. 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 terminated by a spherical extremity, 

 consisting of numerous 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. 



Fifth Period. At this stage the apex of the nucleus, with 

 that of its tegumentary 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 con- 

 stitutes the axis of the embryo. The suspensor is, in a cor- 

 responding degree, lengthened by an increase in the number 

 and size of its cells ; while its upper extremity has now pro- 

 truded 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. 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 



