32 BOTANICAL GAZETTE [JULY 
becomes the archesporium, while the outer, the so-called 
‘tapetum,’ forms a part of the sporangial wall. 
In Rosa’ and Fagus® the epidermis has been found to divide 
several times by periclinal walls, and thus to form a considerable 
portion of the tissue between the archesporium and the apex of ~ 
the nucellus. The unusually large number of cells in this — 
region in Potamogeton at first suggested that the same phenom- 
enon might also be found here; but a careful study showed that 
no divisions of the epidermis beyond an occasional doubling of — 
individual cells ever take place, and all of the tissue can be ~ 
easily traced to the primary wall-cell. Moreover, the similarity 
to the process in the microsporangia is so evident as to require : 
no other explanation. 
ae 
THE FORMATION OF THE EMBRYO-SAC. 
The lowermost cell formed by the first division of the 
hypodermal cell begins to enlarge at once, and must henceforth 
be considered as the archesporium. The whole process during 
the early stages of development is perfectly normal. The 
archesporial cell soon undergoes division resultirig in an upper 
and a lower cell (fig. 75). These probably corfespond to the 
two resulting from the heterotypic division in Convallaria, but 
the fate of the two cells we shall find is somewhat different 
either from that in Convallaria or in Canna. The first division 
is immediately followed by a second nuclear division in each of 
the daughter cells, but without the formation of a wall between 
the two nuclei(fig. 76). The uppermost cell now shows signs 
of disintegration, as indicated by the cytoplasm, which becomes 
more dense and also stains more deeply. The nuciei also lose 
their definite outline, and finally the whole cell becomes much 
compressed and flattened against the wall-cells above. In 4 
very short time, indeed, it can be recognized only as a dark cap 
at the summit of the embryo-sac. Several preparations were 
SSTRASBURGER: Die Angiospermen und die Gymnospermen 14. Jena, 1879: 
°BENSON: Contributions to the embryology of the Amentiferae. Trans. Lint 
Soc. II. Bot. 3: 410. 1894. 
