6 jo Campbell. — Studies on the Araceae. 
considered the normal development. No tapetal cells were 
observed in any case, and the single archesporial cell, or each 
of the two or three cells where more than one embryo-sac 
mother-cell is present, develops at once into the embryo-sac. 
Where two or three young embryo-sacs develop, they may be 
separated by an obliquely transverse wall (Fig. 7), or more 
commonly by oblique or longitudinal walls (Fig. 5). 
Where a single embryo-sac only is present, it enlarges 
rapidly, and the nucleus divides as usual, the two daughter- 
nuclei sometimes at least occupying approximately the micro- 
pylar and antipodal ends of the young sac (Fig. 4). With 
the crowding upon the nucellar cells, their nuclei become 
extraordinarily flattened, assuming the form of thin discs, 
in which the nuclear network is extremely conspicuous 
(Fig. 4, c). After the second nuclear division in the embryo- 
sac, the nuclei may be in pairs at the end of the sac, but this 
is not always the case. In the specimens shown in Fig. 6 the 
four nuclei were close together at the apex of the sac, and 
from other cases examined it is clear that the polarity, so 
marked in the embryo-sac of most Angiosperms, is in this 
case very slight or quite absent. Even where the nuclei are 
in two groups they are more often placed laterally than at the 
extremities of the sac. This is especially true of the group 
from which the egg-cell develops. So far as could be deter- 
mined from the examination of a large number of ovules, the 
characteristic structures of the typical angiospermous embryo- 
sac, the egg-apparatus, polar nuclei, and antipodals are never 
clearly differentiated in Aglaonema commutatum. 
While the number of nuclei is probably eight in most cases, 
there are frequently deviations from this number. In the 
specimen shown in Fig. 8, c, d , e , there were twelve nuclei, in 
three groups of four ; Fig. 18 shows a sac with ten nuclei, six 
in one group and four in the other ; in Fig. 9 is shown a sac 
in which the nuclei were only four, although something like 
an egg-apparatus was evident at the micropylar end of the 
sac. 
Where the archesporium consists of more than one cell, 
