134 BOTANICAL GAZETTE [FEBRUARY 
By the last week in February the cavity of the ovary has considerably 
increased and made room for the growing ovule. At this point the 
differentiation between the nucellus and its integuments begins to 
be noticeable, but as yet there is no division between inner and outer 
integuments. By the first or second week in March the outer integ- 
ument begins to appear, and the inner integument grows up so as 
nearly to cover the nucellus, leaving only a narrow micropyle above 
its tip. An examination of the nucellus at this stage shows that it 
is invested by a distinct outer layer of cells differing from the interior 
cells in their greater regularity of outline. The cell at the tip of the 
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Fic. 1.—Ovule, showing archesporial cell. Fic. 2—Same, after formation of 
two epidermal layers. Fic. 3.—First division of archesporial cell. Fic. 4.—The row 
of megaspores. All X350. 
nucellus and immediately under this investing layer is the arche- 
sporium (jig. 1). At this stage it differs from the surrounding cells 
neither in size nor in the nature of its contents, and can only be dis- 
tinguished by its position. 
As the nucellus grows, the cells of the outer layer divide, forming 
two layers outside the archesporium (fig. 2). The latter then divides 
transversely, cutting off a narrow tapetal cell (fig. 3). Up to this 
point the archesporial cell has undergone very little increase in 
size, but now the primary sporogenous cell begins to lengthen down- 
