1902] EMBRYOLOGY OF LIMNOCHARIS 215 
Very early it is possible to distinguish the single hypodermal 
cell that forms the archesporium (jig. 2). It is somewhat 
larger than the surrounding cells, and the nucleus is consider- 
ably larger than those of the adjacent cells. There is a tapetum 
cut off by the archesporial cell, such as is described by Campbell 
for Naias and Zannichellia. In Limnocharis, however, the 
Tapetal cell is without a wall, and it is pushed towards the apex 
of the sac (fig. 4), where it disappears in the later stages of 
development. The large cell left after the formation of the 
_‘apetum becomes the embryo sac without further division. 
About the time the first division takes place. in the embryo sac 
theepidermal cell that overlies it divides by a periclinal wall, 
forming a false tapetal cell (jig. 2). 
In Butomus, according to 
Ward, there a 
oe re two cells cut off in succession from 
=f» OF the archesporial cells, and sometimes the first one 
divides once longitudinally. These three cells have very deli- 
Tivreat walls, and soon disappear. 
The history of the nuclear changes in the embryo sac differs 
my from the ordinary in the last stages. After the 
= vg of the megaspore nucleus, the two daughter nuclei 
= to each end of the sac. The one that goes to the 
“ar end passes through the usual divisions to form the 
on and upper. polar nucleus ; while the one that. 
_ ,, ttpodal end remains undivided (figs. 5-8). In 
ee Marshall Ward sa — 
ys that sometimes only two nuclei ~ as 
« tthe antipodal end of the sac, and that one of ‘ 
a h the upper polar, leaving only one antipodal. 
Snot cut off by a wall from the sac in Limnocharis, ~ 
isma, while in Sagittaria, Naias, and Zanni- 
are formed around each of the antipodal nuclei. 
fucleus at the micropylar end of the sac 
y (hg. 5), and then each of the resulting — 
tudinally (figs. 6-7), but not always simul-— 
the usual four at that end of the sac. The 
~ ‘WO nuclei, by division, makes the egg and 
or 
i the other forms the two synergids. 2 
