414 



GENERAL MORPHOLOGY OF PLANTS 



form a peripheral layer in the embryo sac and are later sepa- 

 rated by cell walls, thus forming the cellular endosperm. This 

 serves as food for the embryo just as in the case of the Gymno- 

 sperms, but its origin is different. In the formation of the 



Ant 



Fig- 394- Fig. 395. 



Mature embryo sac (young pro- Diagrammatic section of ovary and ovule at time of fer- 



thalhum) of Lihum. m, micropylar tilization in angiosperm. /. funicle of ovule; w, nucellus; 



end; 5, synergids; E, egg; Pn, m , micropyle; b, antipodal cells of embryo sac; e, endo- 



polar nuclei; Ant, antipodals. sperm nucleus; k, egg cell and synergids; at, outer integ- 



(Easter lily.) ument of ovule ; ', inner integument. The track of the 



pollen tube is shown down through the style, walls of 



the ovary to the micropylar end of the embryo sac. 



endosperm the tissue of the nucellus (inner portion of the macro- 

 sporangium) is usually all consumed, leaving only a thin, dead 

 outer portion surrounded by the ovule coats, or integuments. In 

 a few plants, however (water lily family, pepper family, etc.), 

 much of the nucellus remains in the seed as a nutritive tissue 



