360 



GAMETOPHYTE OF ANGIOSPERMS 



in order to prepare a solution suitable for their development. 

 The tube cell, stimulated by the secretion of the stigma, ruptures 

 the outer wall of the spore, which is provided with one or more 

 thin places to favor this growth, and protrudes as a delicate tube. 

 This tube, owing to the fact that it is repelled by the oxygen of 

 the air, grows down into the tissues of the style which are really 

 a continuation of the stigma. These tissues of the style are usu- 

 ally looser and provided with abundant foods which are deposited 

 in the cells just ahead of the elongating tube to nourish and direct 

 it in its growth. In this way the tube is directed down the style 

 to the cavity of the ovary where, owing to the attractive influence 

 of the organic substances in the sporangium, possibly in the syn- 

 ergids, it usually turns out into the cavity of the ovary, enters 

 the micropyle and works its way through the sporangium, and, 

 unlike the Pinales, enters the female gametophyte alongside of 

 one of the synergids (Fig. 273). The antheridial cell usually 



Fig. 273. Section of the micropylar end of the megasporangium, show- 

 ing the process of fertilization. The tube, t, has passed through the micro- 

 pyle, entered the female gametophyte and ruptured, discharging the male 

 gametes. One, <$, is shown fusing with the female gamete. $. and the 

 other one, d", is uniting with the two polar nuclei, thus making a triple 

 fusion in the formation of the endosperm nucleus; s, one of the syner- 

 gids ; i, integuments. 



