334 Campbell. — Studies on the Araceae , III. 
endosperm. The basal cells may divide somewhat further, but the divisions 
are apparently all vertical ones, and the small group of basal endosperm- 
cells thus formed looks very much like a mass of antipodal cells, and might 
very readily be mistaken for them, had not the study of the development 
of this group of cells shown unmistakably that they were the derivatives 
of the lower of the two primary endosperm-cells. The true antipodal 
cells are clearly recognizable up to the time of the first division of the 
endosperm-nucleus, but soon become so crowded upon by the growing 
endosperm as to be no longer distinguishable. 
In one case (Fig. n), above the normal embryo-sac containing the 
egg-apparatus, antipodals, and endosperm-nucleus, there was another cell 
containing four free nuclei. From a comparison with Nephthytis and 
Aglaonema where secondary embryo-sacs frequently occur, it is probable 
that this cell is a second embryo-sac in which the early divisions of the 
nucleus had taken place, but which would probably not reach maturity, 
and would be finally destroyed by the growth of the principal embryo-sac. 
The embryo-sac remains decidedly elongated and of nearly equal 
diameter throughout. The basal endosperm-cells, as we have already 
indicated, divide only by vertical walls and form a mass of tissue sharply 
separated from the much larger cylindrical mass derived from the upper 
cell. While in the latter the earlier divisions are all transverse, later there 
are also formed vertical walls, but these are less numerous than the 
transverse divisions, and the sac retains its narrow form until the embryo 
is far advanced. 
With the growth of the endosperm the lateral tissues of the nucellus 
are quite destroyed, and the apical cap of cells is all that is distinguishable 
of the upper part of the nucellus. While this cap increases somewhat in 
size with the growth of the embryo-sac, it does not keep pace with the 
latter, which finally exceeds it considerably in width. 
In its later stages, therefore, the embryo-sac shows a growth of basal 
endosperm-cells extended vertically, and a much larger mass of thin-walled 
cells with transparent contents and not very large nuclei, this mass of cells 
being derived exclusively from the divisions of the upper of the primary 
endosperm-cells. 
The Embryo. 
The development of the embryo does not begin until the endosperm 
is well advanced in its growth. Traces of the synergidae remain visible 
for a short time, but soon become unrecognizable. The egg enlarges but 
little, and after the membrane is formed about it is nearly hemispherical 
or slightly elongated in outline, and is attached by a broad base to the 
apex of the sac (Fig. 30). The first division-wall is transverse and is 
