1900 | DEVELOPMENT OF THE EMBRYO-SAC 31 
entirely breaks down before the fusion of the polar nuclei, one 
of. which comes from each cell. 
Potamogeton foliosus Raf. 
THE HYPODERMAL CELL AND ARCHESPORIUM. 
In the earliest stage obtained the hypodermal cell at the 
apex of the nucellus had commenced its period of growth. No 
definite form can be ascribed to it at this period, although it is 
perhaps more often wedge-shaped. Even from the beginning it 
usually contains more protoplasm than the other cells, a feature 
which at a later stage becomes still more noticeable. 
After a short period of growth this cell divides. The inner 
daughter cell resulting from the division becomes immediately 
the archesporial cell (fig. 14). The outer daughter cell divides 
again by an anticlinal wall. Two cells now lie side by side 
above the archesporium, as is represented in fig. 12, which 
shows a cross-section through the apex of the nucellus. fig. 
13, also a cross-section of the nucellus taken from the same inflo- 
rescence as fig. 12, shows that each of two cells now divides 
again, so that four daughter cells are formed all in the same 
plane. This last division may take place either before or. after 
the first periclinal division of the wall-cell, commonly however 
before. Periclinal divisions in all four cells now begin, so that 
at length four rows of cells are formed between the arche- 
sporium and the epidermis. The process may continue until as 
many as six layers are produced ; and these all persist until the 
embryo-sac reaches maturity, although often in a more or less 
compressed condition. 
In the anther the hypodermal celi divides into two parts, 
one being destined to produce the archesporium, while the 
other after two or three periclinal divisions constitutes, together 
with the epidermis, the wall of the anther. The stages leading 
up to the production of the embryo-sac in the ovule are in 
many respects very similar to those occurring in the young 
anther. The hypodermal cell here also divides by a peri- 
clinal wall into two daughter cells, the innermost of which 
