SPERM ATOPHYTKS : AXGK ISPEUMS 



the sac becomes more or less filled 

 with nutritive cells, which are 

 often organized into a compact 

 tissue (Fig. 170). These nutri- 

 tive cells correspond to the endo- 

 sperm of Gymnosperms, and re- 

 ceive the same name. In Gymno- 

 sperms, therefore, the endosperm 

 (the nutritive body of the female 

 gametophyte) is mainly formed 

 before fertilization, while in An- 

 giosperms it is mainly formed 

 after fertilization. This means 

 that in Angiosperms eggs are 

 formed and fertilization takes 

 place in a very young gameto- 

 phyte, while in Gymnosperms and 

 heterosporous Pteridophytes the 

 eggs appear much later. 



The antipodal cells also proba- 

 bly represent nutritive cells of the 

 gametophyte. Sometimes they dis- 



FiG. 178. End of embryo-eac of 

 lily (Lilium PhUadelphicum): 

 a pollen tube has entered the 

 sac and has discharged a male 

 cell, whose nucleus is seen 

 uniting with the nucleus of 

 the egg ; near the tip of the 

 tube is the disorganizing nu- 

 cleus of one of the synergids. 

 — Caldwell. 



Fig. 179. One end of the emhryo-sac in wake-robin ( Tt'iUiuni). showing endosperm 

 (shaded cells) in which a young embryo is imbedded. — After Atkinson. 



