FERTILIZATION AXD DOUBLE FERTILIZATION 383 



egg apparatus, of which one, with surrounding protoplasm, con- 

 stitutes the egg, and the other two are called synergids (meaning 

 co-workers). There is a group of three nuclei at the opposite 

 end of the sac, called antipodal nuclei (Fig. 306, B, ant), which 

 frequently become inclosed by delicate walls and possibly repre- 

 sent a prothallial region. The remaining two nuclei, called polar 



s-- 



ant 



FIG. 306. The ovule and embryo sac of the lily 



A, ovule with jnature embryo sac : the inner integument ii has grown beyond the 

 nucellus n; oi, outer integument; m, micropyle. -B, mature embryo sac: egg 

 apparatus at the micropylar end m ; e, egg ; s, synergids ; the two polar nuclei 

 p are about ready to fuse near the center of the sac ; ant, antipodal nuclei 



nuclei (Fig. 306, B, p), pass from the opposite ends to the center 

 of the embryo sac, where they later unite. 



362. Fertilization and double fertilization. The tip of the 

 pollen tube fuses with the end of the embryo sac, near the 

 synergids, and the two sperm nuclei are discharged into the sac. 

 The tube nucleus has generally broken down and disappeared 

 entirely by this time (Fig. 156, F, G). One of the sperm nuclei 

 unites with the egg nucleus (Fig. 307, e, fs), and this is the 

 process of fertilization. 



