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 1 , 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.. 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 
