56 PHARMACEUTICAL BOTANY 



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 ',f.un., 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 



