Dr. Giraud's Contributions to Vegetable Embryology. 165 



at first, of two rows of cells ; the cellular process, with which it is organically 

 united, has reached the base of the ovule ; the cells of its extremity abound 

 in cytoblasts, showing it to be yet progressing in its development. With the 

 increased growth of the embryo two lateral processes are observed proceed- 

 ing, on opposite sides, from the axis, and evidently forming the first traces of 

 the cotyledons (fig. 7, k-)- 



Seventh Period. — All distinction between the nucleus and its tegumentaiy 

 membrane ceases, as they are now united in one envelope inclosing the em- 

 bryo-sac. The cellular process connected with the suspensor has become so 

 much developed, that its extremity has passed around the base of the ovule, 

 and is directed towards the axis of the pistil. The lateral processes of the 

 axis of the embryo have become distinct fleshy cotyledons (fig. 8, «, ra.), ex- 

 tending backwards from their point of origin towards the radicle, as well as 

 forwards in the direction of the plumule ; both which organs they inclose in 

 corresponding depressions in their opposed surfaces. With the development 

 of the radicle (o.) towards the exostome, the opposite extremity of the axis of 

 the embryo (in the form of the plumule) (p.) extends towards the base of the 

 nucleus, but is still inclosed in the depression formed in the concavity of the 

 cotyledons. 



The subsequent changes consist chiefly in the great development of the 

 cotyledons, which ultimately come to occupy the whole cavity of the nucleus, 

 filling the space usually taken up by the albumen. 



The physiological inferences deducible from the foregoing statements are of 

 great interest, as contributing to the determination of many unsettled points 

 involved in the theory of vegetable embryogeny, and also as serving to eluci- 

 date many obscurities relating to the morphology of the embryo. 



It has been shown above, that the formation of the embryo-sac, and the 

 development of cytoblasts within it, takes place at a period prior to the im- 

 pregnation of the pistil ; and that even the primary utricle itself makes its 

 appearance before the emission of the pollen from the anther, and before the 

 expansion of the stigma ; so that the origin of the primary utricle must not 

 be referred to the influence of impregnation, as has been already pointed out 

 by Mirbel and Spach in the case of Zea Mays. At its first appearance, the 

 primary utricle is seen to be quite distinct from the embryo-sac, even at its 



