330 
AMERICAN JOURNAL OF BOTANY 
[Vol. io, 
Development of the Ovule and Embryo Sac 
The ovules are very numerous, completely covering the free surface of 
the placenta. They appear at first as erect, roundish protuberances (text 
fig. 2), but soon become somewhat pointed with the point directed laterally. 
Soon the integument appears as a relatively thick band of tissue closely 
surrounding the base of the central tissue or nucellus (PI. XXV, fig. 4). The 
latter becomes obovate on account of the restriction of growth by the 
integument. The integument grows very rapidly and soon overtops the 
nucellus, which then ceases its growth; the single layer of cells of which the 
nucellus is composed becomes pressed flat against the inner surface of the 
integument and finally disappears. As the embryo sac approaches maturity, 
the inner cell layer of the integument becomes differentiated as a nutritive 
tissue, the cells becoming much enlarged and elongated in a direction 
perpendicular to the surface of the embryo sac (PI. XXVI, fig. 6). This 
nutritive layer is continuous or nearly so with a group of similar but more 
angular cells in the chalaza, against which the embryo sac rests at its base. 
A single branch of vascular tissue from the bundles of the placenta passes 
upward through the funiculus and terminates in the ovule near the chalaza. 
The cells of the integument divide in all directions, producing an extensive 
tissue, and the embryo sac becomes deeply buried. The edges of the 
integument do not actually join over the end of the embryo sac, however, 
so that there remains a narrow and somewhat curved channel, the micro- 
pyle, through which the pollen tube may enter. 
Meanwhile the lateral curvature of the ovule continues, and at length 
the opening of the micropyle is directed downward and is found not far 
from the funiculus. The ovule is not, however, of the typical anatropous 
type, since the embryo sac is considerably curved, suggesting a transition 
to the campylotropous form. 
The archesporium may be distinguished at an early stage in the de¬ 
velopment of the ovule, usually in the form of a single hypodermal cell at the 
apex of the ovule. This cell is distinguished from the neighboring cells by 
its dense contents and deep staining reaction. It may not, when first dis¬ 
cernible, be larger or have a more conspicuous nucleus than the surrounding 
cells. It grows rapidly, however, and the nucleus soon becomes quite 
large. At this stage it may be regarded as a megaspore; further develop¬ 
ment is delayed for a time (PI. XXV, fig. 4). 
As a rule, only a single archesporial cell is produced, though a number 
of ovules were observed containing two or more archesporial cells lying 
side by side, and in a single instance two such cells had developed to what 
may be regarded as the one-nucleate stage of the embryo sac. In nearly 
every case it appears that only one cell develops to the megaspore stage. 
Any other archesporial cells which may be present are crowded out and dis¬ 
appear at an early stage. In a few instances a row of two or three sporo- 
genous cells was found in the axis of the ovule, suggesting a transverse 
