218 Cook : Potamogeton lucens 



13. Schaffner, J. H. Contribution to the life history of Sagittaria 



variabilis. Bot. Gaz. 23: 252-273. //. 20-26. 1897. 



14. Wiegand, K. M, The development of the embryo-sac in some 



monocotyledonous plants. Bot. Gaz. 30 : 25-47. />/. 6, 7. 1900. 



Agricultural Experiment Station, 

 Newark, Delaware. 



Explanation of plates 9 and xo 



Figures I to 13 were made with Bausch & Lomb I -inch eye-piece and 1/12 oil-im- 

 mersion objective. Figures 14 to 24 were made with same eye-piece and 1/6 objective. 

 All have been reduced somewhat more than one half in reproduction. 



Fig. 1. Functional megaspore. 



Fig. 2. Two-nucleate sac. 



Fig. 3. Four-nucleate sac. 



Fig. 4. Eight-nucleate sac. 



Fig. 4a. Complete union of the polar nuclei. 



Fig. 4b. Union of polar nuclei and male nucleus. 



Fig. 5. Sac soon after fertilization. 



Fig. 6. Sac soon after disintegration of the antipodal cells. 



Fig. 7. Sac soon after first division of the primary endosperm-nucleus. 



Fig. 8. Sac soon after first division of the nucleus in the antipodal end of the sac. 



Fig. 9. Sac showing increase in endosperm growth of the nucellar tube nucleus. 



Fig. 10. Nucellar tube nucleus at its maximum in size and activity. 



Fig. 11. Nucellar tube undergoing disintegration. 



Fig. 12. Typical endosperm-cell without walls. 



Fig. 13. Unusual endosperm-cell with walls. 



Fig. 14. Mass of nucellar cells at the antipodal end of the embryo-sac. 



Fig. 15. Young embryo after first longitudinal division of the apical cell. 



Fig. 16. Young embryo slightly older than in Fig. 15. 



Fig. 17. Young embryo slightly older than in Fig. 15. 



Fig. 18. Young embryo, showing three segments. 



Fig. 19. Young embryo, showing three segments, slightly older than in Fig. 18. 



Fig. 20. Young embryo, rather unusual form. 



Fig. 21. Spherical embryo, showing three segments. 



Fig. 22. Spherical embryo, showing three segments, slightly older than in Fig. 21. 



Fig. 23. Embryo, showing the cotyledon and also the large vesicular basal cell in 

 first stages of disintegration. 



Fig. 24. Embryo, showing differentiation of tissues. 







