FERTILIZATION. 169 



the pollen tube with the embryo sac, and the imbibition by the 

 embryonal vesicle of the contents of the pollen grain through 

 the intervening membranes, the vitally active contents of the 

 two cells being thus commingled. 



The development of the embryo. The embryonic vesicle is 

 at first simply a spherical cell, developed at the end of the sus- 

 pensory filament, filled with fluid, and containing granular 

 matter. A little time after fecundation, a longitudinal septum, 

 in the same direction as the suspensor, is seen to form across 

 the cavity of the cell, which thus becomes divided into two cells. 

 Very soon each of these two cells is divided into two others, 

 and all prove successively the same segmentation. The neces- 

 sary result of this is, a little mass of cellular tissue limited 

 exteriorly by the walls of the primitive cell, forming the 

 embryonal vesicle. It is this mass of cellular tissue which by 

 degrees organizes itself into an embryo. 



In some plants it remains in this primitive and somewhat 

 amorphous state, being simply a mass of cells without distinc- 

 tion of organization or of parts. This is its condition in all 

 Acotyledonous or Cryptogamous plants/ where the embryo 

 bears the special name of spore. In Phanerogamous plants, 

 however, this mass of cells assumes a more highly developed 

 state. The cells in the upper part of the mass which are 

 immediately connected with the suspensory filament, elongate 

 into a somewhat conoid body, which in the perfect embryo 

 constitutes the radicle, whilst the cells in the lower part soon 

 begin to present traces of their future cotyledonary character, 

 the end farthest from the suspensor becoming two-lobed in 

 Dicotyledonous, and one-lobed in Monocotyledonous embryos. 

 wv, the name of a plant having leaves like seed-lobes.) 

 15* 



