442 



STRUCTURE AND LIFE HISTORIES 



rise to as many as four embryos (Fig. 325), but usually 

 only one of them develops. 



394. Formation of the Seed. — While the fertilized egg 

 is developing into the embryo, the endosperm-nucleus 



Fig. 328. — Lilium canadense. Embryo-sac at the time of fertilization; 

 a\ a^, antipodal cells; dn., endosperm-nucleus; pi., remains of pollen-tube; 

 e.n., egg-nucleus; s.n.^, sperm-nucleus, fusing with the egg-nucleus; s.n.^, 

 second sperm-nucleus, which may later fuse with the endosperm-nucleus, 

 thereby accomplishing double fertilization. (Redrawn from camera 

 lucida drawing by O. E. White.) 



is undergoing successive, rapid divisions, which finally 

 result in the formation of an abundance of starchy endo- 

 sperm, surrounding the embryo, and serving to nourish it 



