1900] DEVELOPMENT OF THE EMBRYO-SAC 33 
obtained showing the various stages of this process with great 
clearness. 
The lower cell on the other hand continues to enlarge. The 
two nuclei are usually located at opposite ends of the cell and 
are somewhat larger than those of the surrounding tissue (fg. 
77). In the next stage observed both of these nuclei had 
undergone division, so that two were present at each extremity 
of the embryo-sac (fig. 78). At the antipodal end, from this 
stage onward,a small pouch begins to appear which contains the 
two lower nuclei and finally all of the antipodal cells. One of the 
two upper nuclei is now sometimes found slightly below the 
other, and nearer the center of the embryo-sac; but many other 
preparations show that this is merely temporary or abnormal, 
and that before the next stage is completed they are both 
located together at the apex of the cell cavity (fig. 79). 
Very soon after the last nuclear division a cell membrane can 
be seen to form around the two nuclei at the mycropylar end of 
the embryo-sac, thus enclosing them in a little pouch (jig. 
79). The membrane constantly grows thicker, until at length it 
is a distinct wall, and the two nuclei are henceforth entirely 
Separated from the cavity below. This seems to preclude 
entirely the possibility that a polar nucleus may pass down and 
fuse with one from the lower group of cells, although the latter 
remains in the general cavity of the embryo-sac until a much 
later period. 
At a still later stage three nuclei instead of two are to be 
found in the micropylar enclosure (fig. 20). Two of these are 
small and differ but slightly from those of the surrounding tis- 
sue, while the third is much larger and located below close to 
the membrane. It seems probable that the two smaller nuclei 
are produced by the division of one of the two original nuclei, 
and are really to be considered as synergids; while the other 
and larger one is the egg derived directly from the other nucleus 
without division. 
The two nuclei at the antipodal end of the embryo-sac after 
the pouchlike extension has commenced to form usually lie one 
