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 is). 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. 
