1892. ] Development of the Flower. 409 
of the transverse cell walls (fig. 18). The order of nucellar 
displacement begins at the apical end of the nucellus and pro- 
ceeds toward its basal portion (fig. 19); finally, the whole 
nucellar-tissue is displaced and absorbed by the embryo-sac, 
which subsequently becomes very much enlarged. In fig. 1 
is seen a partial obliteration of the nucellus and at this period 
of growtn the embryo-sac is completely filled with protoplasm, 
in the central portion of which is located the mother-cell with 
a vacuole both above and below it. Fig. 20 shows a com- 
plete displacement of the nucellus and elongation of the 
embryo-sac; a farther separation of the vacuoles; the first 
division. of the mother-cell into two daughter cells, each mov- 
ing, the one into the upper, the other into the lower end of 
the embryo-sac. In the next stage of developmert we have 
the first division of the polar nuclei, thus making two nuclei 
in each end of the embryo-sac. The two upper nuclei rest 
within an accumulation of protoplasmic substance, while the 
two lower nuclei rest within a less dense plasma between an 
upper and a lower vacuole which show a longitudinal expan- 
sion (fig. 21). Previous to the last division of the polar nuclei, 
ense 
“Material separating two large vacuoles. Of the three antip- 
_ dal cells remaining, the two upper, which lie alongside and 
impinge on each other, also rest in a plasma bridge separat- 
ing two vacuoles, the upper of which is the larger and the 
Wer one of the two previously mentioned. The lowermost 
ree opposite, but surrounded by a denser mass of seit 
M, Constitute the true egg-apparatus. The two upp 
e 
