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 



l>0 St is 



Fig. 326. — At the left, diagram of the anatomy of an angiospermous 

 flower shortly after pollination; anlh., anther; fd., filament; st., stamen; 

 slig., stigma; p.g., pollen grains germinating; sly., style; pL, pollen tube; 

 o.'co., 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; dial., chalaza; mi., 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). 



