Campbell . — Studies on the Araceae. 683 
is a layer of meristem, which probably serves as the initial 
for all the outer tissues. 
The epidermal cells of the stem-apex are narrower than the 
ordinary epidermal cells (Fig. 55), but otherwise the stem- 
apex is indistinguishable, except from its position. The 
cotyledon constitutes the greater part of the embryo, and its 
base partially encloses the inconspicuous stem-apex, as is 
so often the case among Monocotyledons. 
None of the permanent tissue elements were recognizable 
in the oldest embryos which were available, and only the 
slightest traces of the young vascular bundles could be de- 
tected. The embryo in the ripe seed occupies only a small 
portion of the large embryo-sac, which is filled with the 
endosperm-tissue (Fig. 56). 
As the seed approaches maturity the endosperm-cells de- 
velop numerous small starch-granules. The growing embryo 
uses some of this, so that the cells immediately surrounding 
the embryo contain but little starch, while those in the central 
part of the sac (Fig. 58) contain a great deal. The basal 
cells of the endosperm become much larger than the upper 
ones, and their walls are much thickened, so that they show 
a certain likeness to the enlarged antipodal cells. Like the 
latter, their nuclei are also enlarged, although not nearly to 
the same degree, and show some evidences of disintegration. 
Summary. 
1. In both Aglaonema and Spathicarpa the pistillate flower 
consists of a solitary carpel containing a single basal ovule, 
probably of axial origin. 
2 . The embryo-sac of Aglaonema commutatum shows many 
deviations from the usual type. These consist first in a 
varying number of embryo-sacs, ranging from 1 to 3. Where 
two or three are formed, this may be from a division of a 
common archesporial cell, but in some cases it looks as if 
these originated independently from hypodermal cells. All of 
these embyro-sacs usually undergo the first nuclear divisions, 
but probably only one ever becomes fully developed. The 
