DEVELOPMENT OF PLANTS 377 



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 



Fig. 272. Germination of the microspore: A, mature microspore of lily. 

 B, first stage of germination—;, tube cell; a, antheridial|cell. C, final divi- 

 sion, in this case effected while in the microsporangium — t, tube cell; a, an- 

 theridial cell forming directly two male gametes. D, diagram showing the 

 formation of the tube which grows down the style and finally reaches the 

 female gametophyte. The two male gametes, g, are shown passing down 

 the tube; t, tube nucleus. All the figures in sectional view. 



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 

 divides, forming directly two motionless male gametes during the 

 elongation of the tube, and in other cases the gametes are already 

 formed when the microspores are discharged from their sporan- 

 gia. In none of these cases is there any indication in the division 

 of the antheridial cell of the formation of a wall cell as in the 



