146 O’NEAL: EMBRYO SAC DEVELOPMENT IN OENOTHERA 
Explanation of plates 5 and 6 
PLATE 
Fic. 1. The anlage of the ovule before cell differentiation has begun, 
X 350. 
Fic. 2. A slightly later stage, 350. 
Fic. 3. The young ovule shortly before the appearance of the inner 
iesiiaa initials, X 350. 
1G. 4. A young ovule in which the primordial cell and the inner integ- 
ument initials are shown, X 350. 
Fic. 5. A stage similar to that shown in Fic. 4, in which two primordial 
cells may be seen lying side by side, X 350. 
Fic. 6. A slightly later stage in which the tapetal initial and the primary 
ora cells resulting from the division of the primordial cell are shown, 
] a es 
Fo. 7. An early stage in the d 
. A young ovule showing the Jorge megaspore mother cell, nucellus 
with the devote tapetum, and the inner and outer integuments, X 200. 
1G. 9. The nucellus of a latter stage in which a megaspore mother cell 
and a row sie six tapetal cells are shown, X 350. 
Fic. 10. A megaspore mother cell in the synaptic condition, X 
rat 11. A megaspore mother cell in the late telophase of the first aa 
integument, X 350. 
749. 
Fic. 12. The two gee cells resulting from the first division of the 
megaspore mother cell, 
Fic. 13. A late telophase ar the second division of the second division of 
the megaspore mother cell, X 740. 
Fic. 14. A megaspore tetrad, X 740. 
PLATE 6 
Fic. 15. A nucellus surrounded by the inner integument and containing 
the developing megaspore po a tapetum of eight cells which are still in the 
meristematic condition, « 2 
Fr The young m Sicesiibes with its large nucleus and central vacuole, 
and the three naebeeest cells, X 740. 
Fic. 17. A ma pore, X 740. 
Fic. 18. A Siaatects stage of the embryo sac, X 740. 
Fic. 19. A developing embryo sac with four free ase3: X 740. 
Fic. 20. A mature tetra-nucleate serene sac, 740. 
Fic. 21. A fertilization stage, I 
Fic. 22. A fusion of the (larger) egg cal nucleus and the nucleus of the 
sperm (somewhat idealized), 1800. 
