382 



GENERAL MORPHOLOGY OF PLANTS 



cleus and abundant protoplasm. This cell continues to en- 

 large until it forms a large usually elongated sac, the embryo sac. 

 During its enlargement the nucleus divides by three successive 

 divisions into ei^ht nuclei which have a definite arrangement in 



I'ig. 377- 



Podophyllum peltatum, ovule containing mature embryo sac; two synergids, and eggs at left, 

 endosperm nucleus in center, three antipodal cells at right. 



the embryo sac. At first there are four nuclei at the outer end 

 (next the micropyle, called the micropylar end of embryo sac) , and 



four at the base (called the antip- 

 odal end). But soon one nucleus 

 from each pole (called polar nu- 

 clei) of the embryo sac moves to 

 the center, where they fuse to form 

 the primary endosperm nucleus 

 of the endosperm. This leaves 

 three nuclei in each end of the 

 embryo sac. The three at the 

 base are called antipodals. They 

 Fl ?; j 78 ' usually soon degenerate. The 



Macrospore (one-celled stage) of Lihum. * 



three at the micropylar end are 



called together the egg apparatus. The two nearest the micro- 

 pylar end are called the synergids, which means helpers or co- 

 workers, because it was once thought they assisted the pollen 



