Campbell ’ — Studies on the Araceae , ///. 
343 
The Embryo. 
While the egg-cell is most commonly near the upper end of the 
embryo-sac, it not infrequently is at the side, or even at the base, and the 
position of the embryo varies accordingly. In this respect there is a 
resemblance to Aglaonema. 
When the egg is at the apex it has a broad base of attachment, and 
the first division-wall is nearly parallel to this. No suspensor is developed, 
and the subsequent divisions, which do not appear to follow with absolute 
regularity, transform the embryo into a nearly globular mass of uniform 
cells. Perhaps more frequently the egg-cell is not attached to the wall 
of the sac, and the embryo is then surrounded on all sides by the endo- 
sperm. The older stages of the embryo were not present in the material 
at my disposal, so that the development could not be followed. In the 
ripe seed the embryo constitutes much the greater part. The testa is very 
thin, and the embryo reaches a length of about a centimetre. The greater 
part of the embryo consists of the very massive cotyledon. The root and 
stem are relatively poorly developed. 
The Endosperm. 
The development of the endosperm varies, of course, with the structure 
of the sac at the time of fertilization. Where only one nucleus is present 
besides the egg-apparatus, the endosperm formation begins presumably 
with the division of the sac into two cells, a small basal one and a large 
upper one. Such a case is probably that shown in Fig. 51, in which there 
was, somewhat at one side of the sac, a two-celled embryo, and the sac was 
divided into two cells, of which the lower one was much smaller than the 
other, whose large nucleus was especially conspicuous. 
Where the embryo-sac contains several free nuclei before fertilization, 
it is likely that the endosperm-formation begins by the development of 
membranes between the free nuclei, thus dividing the cavity of the sac into 
several large cells (Figs. 60, 65). In all cases, however, the sac very early 
becomes filled with a continuous large-celled tissue, with the small embryo 
embedded in it. In the older stages the embryo-sac usually shows a 
decided bend near the middle, resembling in this respect, as well as the 
others referred to, the sac of Aglaonema . The lower endosperm-cells 
(Fig. 68) have much denser cytoplasm than the upper ones, and their large 
nuclei show signs of degeneration. It is doubtful whether these basal cells 
are properly to be considered as antipodals, as their exact relation to the 
group of cells sometimes found at the base of the unfertilized sac could not 
be determined. Where there are but two primary endosperm* cells and no 
