SEED-BEARING PLANTS 421 



373. Female Gametophyte. During the first season the 

 megaspore (Fig. 311) enlarges somewhat, and its nucleus 

 divides several times, forming free nuclei. In this condi- 

 tion it remains until the next season, when the formation 

 of the gametophyte is carried to completion. As the 

 gametophyte develops it feeds on the nucellus, which is 

 entirely consumed except for a thin membrane, which 



FIG. 311. White pine (Pinus Strobus). At left, megasporangium with 

 megaspore in the center; above, pollen grains in the micropyle and pollen 

 chamber. At right, pollen grains beginning to germinate; the cells of 

 the integument have enlarged and closed the micropyle. (After Margaret 

 C. Ferguson.) 



adheres to the surface of the gametophyte or endosperm, 

 and a cap of tissue at the tip of the gametophyte (Figs. 

 309, K, and 3 1 2) - 1 The archegonia, two to five in number, 

 at the micropylar end of the gametophyte, are mature by 

 the last of May or forepart of June, in the northern states. 

 In Pinus the neck of the archegonium is very much re- 



1 In the seeds of some of the higher plants the tissue of the nucellus 

 becomes filled with nourishment stored for the use of the developing 

 embryo, during germination. It is then called perisperm. 



