440 



STRUCTURE AND LIFE HISTORIES 



its nucleus undergoing divisions, forming, in succession, 

 a two-celled, four-celled, and eight-celled embryo-sac 

 (Figs. 325 and 326). Three of these cells pass to one 

 end of the sac, opposite the micropyle, and are known 



FIG. 326. At the left, diagram of the anatomy of an angiospermous 

 flower shortly after pollination; anih., anther; fil., filament; st., stamen; 

 stig., stigma; p.g., pollen grains germinating; sty., style; pt., pollen tube; 

 o.w. t ovary wall; o., ovule, containing embryo-sac; pet., petal; sep., sepal. 

 1-8, Stages in the development of the female gametophyte (embryo-sac); 

 meg.sp., megaspore-mother-cell; i.i., inner integument; o.i., outer integu- 

 ment; fun., funiculus; chal., chalaza; nu., nucellus (megasporangium) ; 

 emb., embryo-sac. All diagrammatic. 



as the antipodal cells, or antipodals, while two of them meet 

 in the center and fuse, forming the endosperm-nucleus. 

 The remaining three pass to the end near the micropyle, 

 where one of them becomes organized as the egg-cell; the 

 others are called synergids (helpers) (Cf. Fig. 326). 



