O’NEAL: EMBRYO SAC DEVELOPMENT IN OENOTHERA 139 
The archesporial cell soon divides in a plane at right angles 
to its long axis into an outer cell that functions as ‘a tapetum 
initial and an inner one that becomes the primary sporogenous, 
or megaspore mother cell, Fic. 6. Shortly after the division of 
the archesporial cell the initial development of the outer integ- 
ument may be observed. Fic. 7 shows a section of an ovule 
in which the development of the outer integument is fairly well 
advanced. 
As shown in Fics. 1-6 the young ovule very early in its 
development appears bent upon its growing stalk. This cur- 
vature becomes accentuated as the integuments arise. As 
pointed out above, the inner integument begins as a single 
encircling row of cells that may be recognized by their larger 
size and location as well as by their subsequent behavior; the 
outer integument arises in a similar manner with the exception 
that, as shown in Fic. 7, the initial ring at first is not closed on 
the side next to the funiculus. Fic. 8 shows the ovule at the 
time that the integuments have just reached the end of the 
nucellus. In this ovule the outer integument completely sur- 
rounds the inner envelope of the nucellus. The megaspore 
mother cell with its large nucellus and dense cytoplasm is very 
prominent at this time and the developing tapetum, composed 
in this section of a row of three cells, may be made out also. 
In Fic. 9 a nucellus containing the large megaspore mother 
cell and a row of six tapetal cells is shown. 
Development of the megaspore.—As shown in the figures, the 
large elongate megaspore mother cell is deeply imbedded in the 
nucellus. In some instances, when it begins to divide, a dozen 
cells may be counted in the tapetal row. The cell has pointed 
ends and a large nucleus. The cells at hand do not show the 
resting linin-chromatin reticulum well. While no consistent 
attempt was made to secure a complete set of mitotic figures 
in the division of this cell, practically all of those usually 
described have been found, and some of them, including that 
of synapsis shown in Fic. 10, were observed repeatedly. This 
condition in part at least may be due to faulty fixation. The 
chromosomes are usually in the form of short rods and look 
quite similar to those recently described by the writer (23) for 
Datura. They have been adequately described for this plant 
by Gates (14) in his study of the reduction division of the 
