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 1 , a 2 , antipodal cells; dn., endosperm-nucleus; pt., remains of pollen-tube; 

 e.n., egg-nucleus; s.n. 1 , sperm-nucleus, fusing with the egg-nucleus; s.n. 2 , 

 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 



