GAMETOPHYTE AND SPOROPHYTE. 



233 



into a great many nuclei in a mass of protoplasm, and cell walls 

 are formed separating them into cells. This mass of cells is the 

 endosperm, and it surrounds the 

 embryo. It is the mature female 

 prothallium, belated in its growth 

 in the angiosperms, usually de- 

 veloping only when fertilization 

 takes place, and its use has been 

 assured. 



460. Seed. — As the embryo 



Fig- 3°5- 



Mature embryo sac (young pro- 

 thallium) of lilium. m, micropylar 

 end ; S, synergids ; E, egg ; Pn, 

 polar nuclei ; A ?it, antipodals. 

 (Easter lily.) 



Fig. 306.' 



Section through nucellus and upper part of embryo 

 sac of cotton at time of entrance of pc.llen tube. E, 

 egg: .S", synergids; P, pollen tube with sperm cell in 

 the end. (Duggar.) 



