86 BOTANY AND PHARMACOGNOSY. 



Male Gametophyte. — Before the dispersal of the pollen 

 grains or microspores, certain changes leading to the development 

 of the gametophyte have taken place (Fig. 55). The spore as we 

 have seen is unicellular. This divides into two cells, one, which is 

 relatively small, known as the mother cell of the antheridium 

 (Fig. 55, v), and another, which, composed of the remaining 

 nucleus with the surrounding cell-contents, constitutes the tube- or 

 wall-cell of'the .antheridium. 



Development of Ovule and Megasporangium (nucellus). — 

 The ovule at first develops as a small protuberance on the 

 inner surface of the ovary, after which it differentiates into 



(a) a stalk or funiculus by which it is attached to the ovary, 

 the tissue to which it is attached being called the placenta; and 



(b) an upper portion which becomes the ovule proper. The 

 differentiation of the tissues is in a general way as follows : ( i ) 

 The cells beneath the epidermis in the apical portion of the ovule 

 go to make up the megasporangium (nucellus) ; (2) the periph- 

 eral cells from below the nucellus give rise to the integuments ; 

 and (3) while the integuments are developing the archesporium 

 or mother cell of the embryo-sac (megaspore) is being formed 

 within the nucellus near the apex. 



Female Gametophyte. — The archesporium divides into 

 two cells, the lower one of which repeatedly divides, finally giving 

 rise to the embryo-sac which is sunk in the tissues of the nucellus. 

 The nucleus of the embryo-sac divides and redivides until 8 cells 

 are produced (Figs. 56 and 85), which are separated into the 

 following groups : ( i ) Three of the cells form a group lying 

 at the apex, the lower cell of the group being the egg or egg-cell, 

 the other two cells being known as synergids or helping cells. 

 (2) At the opposite end of the sac are three cells, known as an- 

 tipodal cells, which usually develop a wall of cellulose and do not 

 seem to have any special function. (3) Near the center of the 

 sac are the two remaining nuclei, which unite to form a single 

 nucleus, from which after fertilization the endosperm is derived. 

 The embryo-sac, as it is organized at this stage, constitutes what 

 is regarded as the female gametophyte (Fig. 56). The undiffer- 

 entiated embryo-sac constitutes the megaspore, which latter after 

 germination or differentiation into egg-cell and other cells, con- 



