464 SPERMATOPHYTES (SEED PLANTS) 
region enclosed within the cell membrane of the germinating 
megaspore. In this position nuclear division follows until there 
are four nuclei at each end. The megaspore has now become the 
female gametophyte consisting of eight nuclei, four at the 
micropylar and four at the opposite end, known as the chalazal 
or antipodal end of the embryo sac. After the stage with eight 
nuclei is reached, then the organization of the female gameto- 
phyte begins as shown in Figure 410. A nucleus called polar 
nucleus from each end of the 
embryo sac moves toward 
the center of the sac until the 
two come in contact. Some- 
times they fuse soon after 
coming in contact to form 
the primary endosperm nu- 
cleus, but often they remain 
in contact until fertilization 
and then fuse at the same 
time they fuse with the 
sperm to form the endo- 
sperm nucleus. The three 
nuclei and adjacent cyto- 
: ee plasm at the micropylar end 
Fic. 410. — Organization of the female 
gametophyte in Red Clover. At the left, are organized are three 
a section through the nucellus, showing naked cells, the inner one 
eight nuclei of the female gametophyte being the egg and the other 
with four nuclei at each end of the em- twothe synergids. The three 
bryosac. Atthe right, the gametophyte yyclei at the antipodal end 
fully organized, showing the antipodals ; 
and known as_ antipodals 
at a, the polars at p, the egg at e, and 
the synergids at s. usually disappear early, but 
in some Angiosperms they 
become organized with the adjacent cytoplasm into cells that 
seem to have an absorptive function. The female gametophyte 
is now organized and ready for fertilization. When compared 
with the female gametophyte of the Pine, its remarkable reduc- 
tion in number of cells, the absence of archegonia, and the forma- 
tion of a nucleus for providing endosperm are notable features. 
Male Gametophyte and Fertilization. — On the stigma the 
pollen grain develops a tube which by means of enzymes eats its 
way through the stigma, style, and ovule into the embryo sac. 
s 
