ANGIOSPERMZ 
179 
spore or embryo-sac (Fig. 44, A, ma, B), which in its 
origin corresponds closely to that in the Gymnosperms 
and in such Pteri- 
dophytes as Isoétes. 
As in the Gymno- 
sperms, the macro- 
spore remains per- 
manently within 
the ovule. The 
gametophyte isusu- 
ally extremely re- 
duced, showing in 
the typical forms 
@ very constant 
structure. 
The single nu- 
cleus of the ma- 
crospore divides, 
and one of the two 
resulting nuclei 
moves to each end 
of the spore-cavity 
or embryo-sac. 
Here each nucleus 
divides twice, so 
that there result 
four nuclei at each 
end of the sac. 
Three of them re- 
main at the ends, 
Fia. 44.—A, diagram showing the arrange- 
ment of parts in a typical angiospermous 
flower ; ca, the calyx made up of individual 
leaves, sepals; co, the corolla, composed of 
petals; an, the andrecium, composed of 
the stamens; gy, the gyneecium, made up 
of the carpels (here but a single carpel). 
The upper part, anther, an, of each stamen 
has usually four microsporangia, or pollen- 
sacs; the macrosporangia, or ovules, are 
contained in the ovary, formed by the base 
of the carpel, or united carpels ; p, a pol- 
len-spore germinating upon the stigma, and 
sending its tube, pt, down through the cen- 
tral part of the gyneecium or pistil ; B, dia- 
gram showing the structures within the 
embryo-sac at the time of fertilization. 
The three cells at the upper end form the 
‘‘egg-apparatus,”’ consisting of the two 
synergids, sy, and the egg-cell,o. At the 
lower end are the three ‘“ antipodal-cells,” 
ant, and in the centre are the two “ polar 
nuclei,” pn, which afterward unite into a 
single one, the ‘“‘endosperm-nucleus’’; C, 
young pollen-spore of Naias, showing the 
antheridial cell, x; D, a germinating pollen- 
spore of the sweet-pea; pt, pollen-tube; x, 
sperm-nucleus. 
while the fourth one from each end moves toward the 
centre of the embryo-sac where these two “ polar nuclei” 
