SEED-BEARING PLANTS 



439 



392. The Female Gametophyte. Megaspores are 

 probably not formed in tetrads by two divisions of a 

 megaspore-mother-cell, but the ancestral-cell of the female 



..em. 



FIG. 325. Dog's-tooth violet (Erythronium). i, embryo-sac, binucle- 

 ate stage, the two nuclei dividing; 2, four nucleate stage; 3, mature embryo- 

 sac (es); the pollen-tube (p.l) has reached the egg-apparatus and fertiliza- 

 tion has just taken place; the male and female nuclei are both visible in 

 the fertilized egg. The synergids are not shown; 4, polyembryony; four 

 embryos have developed from the embryogenous tissue, one embryo at 

 the left of a not shaded; 5, longitudinal section of an embryo (em); s, 

 suspensor; i, 2, and 5, E. albidum (after Schaffner); 3 and 4, E. americanum 

 (after Jeffrey). Only one of the multiple embryos persists. 



gametophyte (archesporial cell) functions directly as a 

 megaspore, without division. In very early spring the 

 megaspore begins to germinate, increasing in size, and 



