476 PHARMACEUTICAL BOTANY 
ting forth a tube (pollen tube). The pollen tubes, each carrying 
within it two sperm nuclei and a tube nucleus embedded in 
protoplasm, penetrate through the style canal until they reach 
the micropyles of various ovules. Each enters and passes through 
a micropyle, then piercing the nucellus, grows toward the 
embryo sac. The tip of the tube fuses with the end of the embryo 
sac and the two sperm nuclei are discharged into the sac. One 
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Fic. 358.—At the left, diagram of the anatomy of an angiospermous flower 
shortly after pollination; anth., anther; fil., filament; s¢., stamen; stig., stigma; 
p.g., pollen grains germinating; sty., style; pt., pollen tube; 0.w., ovary wall; o. 
ovule, containing embryo-sac; fet., petal; sep., sepal. 1-8, Stages in the develop- 
ment of the female gametophyte (embryo-sac); meg.sp., megaspore-mother-cell; 
i.2., inner integument; 0.7., outer integument; fun, funiculus; chal., chalaza; nu., 
nucellus (megasporangium); emb., embryo-sac. All diagrammatic, (Gager.) 
of these sperm nuclei (containing x chromosomes) passes between 
the synergids and fuses with the nucleus of the egg (containing x 
chromosomes) to form an oéspore or zygote in which the 2x number 
of chromosomes found in the sporophyte of the species is restored. 
By this time the tube nucleus has disintegrated. The odspore by 
repeated divisions develops into as many as four embryos or 
young sporophyte plants. Only one of these, however, persists. 
The polar nuclei fuse to form the endosperm nucleus which soon 
foe aes 
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