FEMALE GAMETOPHYTE 



455 



extends beyond the nucellus, and its free niai'gin flares open, thus 

 forniin<^ an open inic.ropyle that leads into the pollen chamber. 



Female Gametophyte. — ^ Although four niegaspores are formed 

 in the megasporangium, only one of them develops a gameto- 

 phyte, the others being destroyed and used for food by the one 

 that develops. During the first season the surviving megaspore 

 enlarges and becomes multinucleate. With the megaspore in this 



Fig. 404. — Development of the ovule and pollen tubes in the Pine. C, 

 section through an ovuliferous scale, showing the bract behind and a section 

 of an ovule (s) on its inner face, the megaspore being shown at m; D, an 

 ovule with female gametophyte (/) mature, showing eggs at e, ovule wall 

 consisting of nucellus and integument at w, and pollen grains growing tubes 

 through the nucellus at (p). 



condition the ovule passes the winter. Early next spring growth 

 is resumed, and by about the first of June of the second season 

 the gametophyte is complete, consisting of 250 or more cells and 

 bearing a number of archegonia (usually two to five) at the 

 micropylar end {Fiy. 404-) The eggs are usually ready for 

 fertilization about the first of June of the second season. While 

 the female gametophyte is developing, the male gametophyte is 

 completing its development in the pollen chamber and the pollen 



