254 



BOTANY. 



cell), the other two, the synergids, are sterile. The nuclei 

 at the base constitute a rudimentary sexual plant (prothal- 

 lium) which does not develop until much later. Since the 

 tissues of the ovule-body can sufficiently nourish the germ- 

 cell, there is no need of a prothallium at this time, and 

 there is also an almost complete suppression of the arche- 

 gone-walls. 



479. Fertilization takes place as follows : The pollen-cell, 

 resting upon the moist surface of the stigma, germinates, 

 and its tube penetrates the soft tissues of the stigma and 

 style, finally reaching the cavity of the ovary, where it 

 enters the ovule through the opening in the coats (Fig. 

 152, A). Here it comes in contact with the apex of the 



Fig. 152.— a, a longitudinal section of an ovule of the Pansy, after fer- 

 tilization ; a and ?, coats of the ovule ; p, pollen-tube : e, embryo-sa.c, 

 with the very young embryo at one end and free endosperm-cells at the 

 other. B, apex of embryo-sac, e ; eb, very young embryo of four cells. 



ovule-body, and soon reaches the embryo-sac. The gener- 

 ative nucleus of the pollen-tube unites with the germ-cell, 

 which then forms a wall about itself ; it then divides 

 transversely one or more times, forming a row of cells (the 

 suspensor), at the end of which an embryo soon begins to 

 form by the fission of cells in three planes (Figs. 153, B, 

 and 153, Fto IV). 



480. At first the embryo is a minute rounded cell-mass 

 attached to the end of the row of cells, and in some plants 

 it passes but little beyond this stage until after the ripen- 



