THE SPERMATOPHYTES 451 
tion of the cytoplasm and ultimately cell walls are laid down and 
the entire embryo-sac contains endosperm (prothallial) tissue. 
Toward the micropylar end of the endosperm (frothallus) 
originate several archegonia. 
_Antheridial 
ae Cell 
ik Spong 
He Tice 
Fic. 339.—Longitudinal section of one-year old ovule of Austrian Pine showing 
- jmternal structure. (Mottier.) 
Each archegonium consists of a much-reduced neck of four 
cells and an egg (ovum) which lies embedded in the prothallus 
which forms a narrow layer of cells around it called the jacket. 
The contents of the mature embryo-sac constitutes the female gametophyte. 
