290 Seaton : Embryo-sac of Nymphaea advena 



Explanation of plates IS and ±9 



All figures were drawn with the aid of an Abb6 camera lucida. 



Fig. I. Nucellus with archesporial cell. 



Fig. 2. Archesporial cell dividing. 



Fig. 3. The primary parietal cell and the megaspore mother-cell. 



Fig. 4. Two parietal cells and the megaspore mother-cell. 



Fig. 5. The enlarged megaspore mother-cell. 



Fig. 6. The megaspore mother-cell buried four cells deep by the increase of 

 parietal tissue. 



Figs. 7 and 8. The dividing micropylar cell in the axial row of megaspore-cells. 



Fig. 9. The functional megaspore, with the degenerating functionless megaspores. 



Fig. 10. The division of the embryo-sac mother-cell. 



Fig. 11. The two-nucleate stage of the embryo-sac. 



Fig. 12. The simultaneous division of the two nuclei to form the four-nucleate sac. 



Fig. 13. An ovule with a mature embryo-sac, after fusion of polars and disappear- 

 ance of antipodals ; showing the position in ovule and relative size of the sac. 



Fig. 14. Entire embryo-sac, showing characteristic appearance and arrangement 

 of sac-nuclei just after fertilization. 



Fig. 15. Mature embryo-sac, showing egg-apparatus and endosperm-nucleus. 



Fig. 16. An ovule, showing embryo-sac ready for fertilization. 



Fig. 17. Upper end of a sac, showing condensed cells between sac and the 



micropyle. 



sperm 



Fig. 18. The upper part of sac no. 14, showing details. 



Fig. 19. The lower part of sac no. 14, showing details. 



Fig. 20. The embryo with endosperm tissue and perisperm tissue containing starch. 



Fig. 21. The chalazal end of ovule in 20, showing the persisting lower endo- 



