1896.] Embryo-sac of Alisma, 127 
generally much contorted before reaching the micropyle, 
through the middle of which it finally passes to the top of 
the embryo-sac. Just before the entrance of the pollen tube 
into the micropyle, the two synergida, as stated before, lie 
at the summit of the embryo-sac, with the oosphere sus- 
pended below. The tube in passing through the micropyle 
isconsiderably constricted, but when it reaches the embryo- 
sac it increases appreciably in diameter (fig. 14). On reach- 
Ing the apex of the sac, the pollen-tube does not grow 
directly toward the oosphere, but always passes down on one 
side near the wall of the embryo-sac encountering the nucleus 
of one of the synergide on its passage, which disappears at 
thistime. The tube passes by the nucleus and seems to be 
nourished by its contents. At a certain stage the outline of 
the nucleus and its nucleolus can still be distinguished, but 
it takes little or no stain (fig. 15). 
The nucleus of the other synergida persists for a long time, 
at least until the proembryo is composed of several cells. The 
Pollen-tube after entering the embryo-sac takes a very dark- 
red stain and in it can be distinguished two small nuclei, which 
— exactly like those in the mature pollen-grain. The 
uppe 
complished (figs. 18, 19). The pollen-tube usually curves 
“oe the oosphere before the sperm nucleus leaves it 
g. 17), 
in n the meantime changes are taking place in the oosphere. 
, since at this stage they are farther from the 
Into a c 
it will b 
Seen that a ctable bulge (figs. 13, 16, 17). Thus it will be 
at all the preliminary stages in the approach of the 
