20 THE COMPARATIVE EMBRYOLOGY OF THE RUBIACEAE 
see. In some genera they persist for some time, and vestiges may 
. be seen after a large mass of endosperm has been formed. After 
the megaspore mass is absorbed, the basal antipodal appears to 
have no further function. 
When the embryo starts to develop a small amount of starch is — 
found in the integument, principally in those cells above referred 
to which form a zone between the funicle and the meristem of the 
integument. A very few granules are also to be found in the cells 
immediately about the embryo-sac. As the seed approaches ma- 
turity the starch accumulates first in the peripheral cells until all 
those cells of the integument which remain are replete. 
THE GROWTH OF THE ENDOSPERM 
During the first division of the endosperm nucleus the endo- 
sperm enlarges, becoming rounded, and encroaches upon the ad- 
jacent tissue of the integument, the cells of which become flattened 
and give way. At first, separating walls between the cells are not 
formed. The nuclei are not parietal, nor do they ever become 
so. -The endosperm mass is always solid. A little later the 
parietal cells become much more densely filled with cytoplasm 
and stain more deeply (Pl. 3, Figs. 20, 2c). This is especially true 
of those cells on the side of the endosperm mass facing the longi- 
tudinal ‘axis of the ovary, which are the earliest to become dense. 
It is on this side that the thickness of the integument is the greatest 
and where the food is most abundant. After the endosperm ap- 
proaches its limit of growth, these are the last of the peripheral 
cells to lose their dense character. The inner cells of the endo- 
sperm are strongly vacuolated, the vacuolation becoming more 
pronounced towards the center, where the cells ultimately break 
down and leave a cavity within which lies the now rapidly matur- 
ing embryo. The peripheral cells are digestive, I believe, and ab- 
sorptive, for the integuments break down in advance of the growth 
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of the endosperm, and the cell walls of the disorganized cells be- _ 
come thickened. These thickened walls stain readily and deeply 
with safranin, while the walls of the normal cells show much less 
affinity for that stain. 
As the endosperm ages it becomes concave on its inner 
face, and dipping into the concavity is a mass of integument which 
