ANDERSO:: EMBRYOGENY OF MARTYNIA LOUISIANA 147 
typical axial row of four megaspores is finally formed (Fic. 22), 
and, as is usually the case, the innermost megaspore, the one 
next the chalazal end, persists to form the embryo-sac (Fics. 
22 and 23). The upper three potential megaspores are soon 
destroyed by the rapid growth of the functional one (Fic. 23.) 
By the time the tetrad is formed, the nucellus has reached 
its maximum growth, and the cells of the integument adjacent 
to the nucellus have become dense in cytoplasm and now func- 
tion as a nutritive jacket (Fic. 22). In the meantime the 
integument has grown and exceeds considerably the length of - 
the nucellus (Fic. 23). 
The functional megaspore does not increase much in size 
before the first nuclear division but, after this first division, it 
elongates rapidly and occupies a space almost the length of 
the nucellus (Fics. 23 and 24). As the megaspore elongates 
the two nuclei keep their relative positions—one in each end 
of the cell. Most of the cytoplasm of the cell is in the ends, 
thus leaving a large vacuole in the center. A few strands of 
cytoplasm penetrate the vacuole and form a connection between 
the masses at each end of the cell. The rapid growth of this 
cell has consumed the three upper potential megaspores and the 
nucellus around the center of the spore (FIG. 24). Before the 
second nuclear division of the megaspore takes place, the upper 
three megaspores have practically disappeared and the functional 
one now extends nearly the length of the nucellus, which is rapid- 
ly being used as food (Fic. 25). At this time the central vacuole 
is not so pronounced—at least in some cases. The spindles of 
the second nuclear division may be seen—one in each end of the 
cell. With the exception of a few cells at the chalazal end, the 
nucellus is consumed by the growing megaspore, which comes 
to occupy the space left by the disorganizing tissue. There 
is no evidence of a nucellar cap being formed as Merrell reported 
for Silphium (3) and other plants that have a similar develop- 
ment. The nuclei now undergo another division which results 
in eight nuclei—four in each end of the cell. Next follows the 
formation of the three cells of the egg-apparatus and the three 
antipodals. One nucleus from each end of the embryo-sac, the 
polar nuclei, remains free in the cytoplasm. At this stage, the 
embryo-sac is considerably elongated, being about seven times as 
long as wide. The micropylar end, containing the egg-apparatus, 
is enlarged to about one and a half times the diameter of the 
Other part of thesac. This enlarged portion comprises nearly one 
