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140 O’NEAL: EMBRYO SAC DEVELOPMENT IN OENOTHERA 
microsporocytes. The reduced number seems to be seven, as 
has been reported by other writers; at least, no more than this 
number could be found. The diminutive chromosome reported 
by Lutz (20) for the Amsterdam plant was not found in the 
material studied. FIG. 11 shows a reconstruction -stage in 
which the chromosomes, connecting fibers, and anastomosing 
strands of cytoplasm stand out with particular clearness. 
Fic. 12 shows a little later stage in which the cell wall of the 
first division has been laid down. Fic. 13 shows a stage in the 
second division similar to that of the first division shown in 
Fic. 11. The four potential megaspores are shown in FIG. 14. 
Shortly after the formation of the megaspore tetrad one of the 
four cells begins the development of the megaspore. The cell 
nearest the micropyle is usually the functional one but, in some 
cases, the one at the opposite end of the row develops. This is 
the reverse of the condition found by Davis (6) in Oe. biennis. 
Geerts (15) reported that in Oe. Lamarckiana the cell nearest 
the micropyle is always the functional one of the tetrad. Ishi- 
kawa (17) found that in Oe. pycnocarpa and Oe. nutans the 
cell at one end of the row is just as likely to develop as the one 
at the other, and that either of the two intervening cells may 
develop, while in certain cases two of the cells in a tetrad may 
develop simultaneously. In Oe. rubrinervis the development of 
the cell towards the micropyle places the megaspore nearer the 
center of the nucellus. PLATE 6, FIG. 15, shows the condition 
of the ovule at the time the megasgore is being developed. 
The tapetum in this section is composed of eight cells which 
are still in the meristematic condition. Some sections show a 
greater amount of tapetal tissue than the one represented in 
the drawing. The figure does not show the outer integument. 
Early in the development of the megaspore the nucleus 
migrates to the end of the cell next to the micropyle and a 
conspicuous vacuole appears. The nucleus remains in this posi- 
tion and the vacuole persists until the megaspore is mature. 
Fic. 16 shows a developing megaspore as well as the three 
disintegrating sister cells. 
Germination of the megaspore—FiG. 17 shows a longitudinal 
section of a mature megaspore in which the large nucleus and 
the central vacuole stand out prominently. This vacuole 
which appeared in the development of the megaspore is present 
