IOWA ACADEMY OF SCIENCES. 
213 
embryo sac, ready for fertilization, measures approxi- 
mately 52 u in length and 22 u in width, and occupies 
much less than one-third of the length of the nucellus in 
the one to the four-celled archisporial stage. There are 
generally about two layers of cells of nucellar tissue 
between the archisporium and the dermatogen of the 
nucellus (Fig. 3-6). From the four-celled archisporium to 
the two-celled embryo sac there is generally one layer of 
cells between the macrospore and the dermatogen, and by 
the time the embryo sac has reached the four-celled stage, 
the tapetal end of it is in close connection with the derma- 
togen, there being no tissue between the two. 
At about the time the pollen tube enters the egg cell one 
of the synergids disappears. The other one remains 
apparently unchanged until the process of fertilization is 
completed, after which it is no longer present. The fusion 
of the generative pollen nucleus with the egg cell and the 
fusion vegetative nudes with the endosperm nucleus seem 
to occur at about the same time. The fertilized egg cell, 
before any division takes place, measures about 33 u long 
by 1F| u wide. The endesperm nucleus divides once 
before the first division of the egg nucleus takes place; 
the first division of the endosperm being in the direction 
of the long axis of the embryo sac. The second division 
is at right angles to the first, and it occurs at or just before 
the time that the egg nucleus divides the first time. The 
third division occurs in the lower two cells, resulting from 
the second division, and also occurs in the same direction 
as the second (Figs. 15, 16). The upper cells resulting 
from the first division do not divide until two or three 
divisions have taken place in the lower cells. But by the 
time the embryo has reached the four-celled stage the 
endosperm has extended well up along the side of the 
embryo (Fig. 17). 
The first division of the egg cell is at right angles to the 
long axis of the cell, and it is the lower one of these cells 
that gives rise to the embryo. The upper one forms the 
suspensor. The embryo cell now divides once transversely. 
i. e., in same direction of first division of egg cell. 
