PHARMACEUTICAL BOTANY 
56 
POLLINATION AND FERTILIZATION 
The mature pollen grains are discharged from the ripened anther 
through the splitting open of its wall. They are transferred to the 
stigma of the -pistil of another Erythronium flower through the 
agency of insects. Here they germinate, each putting forth a tube 
Fig. 28. —At the left, diagram of the anatomy of an angiospermous flower 
shortly after pollination; anth., anther; fil., filament; st., stamen; stig., stigma; 
p.g., pollen grains germinating; sty., style; pt., pollen tube; o.w., ovary wall; o. 
ovule, containing embryo-sac; pet., petal; sep., sepal. 1-8, Stages in the devel¬ 
opment of the female gametophyte (embryo-sac); meg.sp., megaspore-mother¬ 
cell; i.i., inner integument; o.i., outer integument; fun., funiculus; chal., chalaza; 
nu., nucellus (megasporangium); emb., embryo-sac. All diagrammatic. (Gager.) 
(pollen tube). The pollen tubes, 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 of these sperm nuclei passes between 
