Jan., 1906.] Embryo Sac and Embryo of Cucumis sativus. 
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megaspore begins to enlarge (Figs. 11-12). The latter acquires 
a very large and distinct nucleus with a nucleolus of unusual 
size. Kirkwood reported to have found in Trichosanthes that 
after the division of the megasporocyte the upper cell did not 
again divide but immediately disorganized, while the lower cell 
again divided transversely, the upper cell of which also disor- 
ganized. The ultimate result, however, is the same in both 
Cucumis sativus and Trichosanthes, that is, the lowest of the 
megaspores always becomes the functional one. 
The embryo sac and its associated structures are quite small 
in comparison with the very large nucellus. The development 
proceeds in the normal way, by a longitudinal division of the 
nucleus of the megaspore (Fig. 13). At this stage often the 
potential megaspores have not completed their dissolution and 
remains of the third one can be seen just above the sac. The 
nuclei arrange themselves at either end of the sac in the center 
of which is a vacuole across which strands of protoplasm may 
extend. In the four-celled stage the large irregular vacuole in 
the center is also prominent. By two successive divisions the 
eight-celled embryo sac is formed (Figs. 14-l.a). The synergids 
are distinct and lie above the egg. In the early stage they are 
somewhat globular in shape and follow the outline of the sac. 
They lengthen considerably and at the time of fertilization they 
are quite long, sac-like structures. The egg is large and extends 
below the synergids, at first merely protruding a little beyond 
their base, but before fertilization it becomes much elongated and 
swollen (Fig. 17). The polar nuclei are unequal in size, the 
lower one being the larger. They conjugate before the entrance 
of the pollen tube. No case of double fertilization was observed ; 
if it occurs it must take place sometime after the polar nuclei are 
in contact. The antipodals are small cells which lie side by side, 
in the lower end of the sac. They take the stain more deeply 
than does the egg apparatus, and for this reason it is often 
difficult to make out their outline. They do not enlarge but 
remain in place and are quite distinct even after considerable 
endosperm has developed. 
The development of the embryo is quite irregular. The first 
division of the oospore is transverse and the upper cell does not 
divide further and may be regarded as a rudimentary suspensor 
(Fig. 18). At this stage the synergids have begun to dissolve. 
The second division is by a longitudinal wall, the lower cell alone 
dividing. Later, one of the lower cells divides by a more or less 
oblique wall forming a four-celled embryo (Fig. 19) which is 
almost surrounded by endosperm. Above the embryo the 
remains of the two synergids can still be seen, although almost 
dissolved at this time. 
