i68 
MORPHOLOGY 
but among the Polypodiaceae usually only the nucleus divides, resulting 
in a single binucleate neck canal cell. The primary ventral cell divides, 
as usual, into the ventral canal cell and the egg (fig. 393, c). In passing 
from Marattiaceae to Polypodiaceae, one passes from broad canal cells 
to small ones, and from two distinct neck canal cells to the elimination of 
the wall (binucleate condition). There is thus a gradual disappearance 
FlG. 393. Archegonium of a fern: a, young stage, showing two neck cells, central 
cell (shaded), and basal cell, all from single initial; b, older stage, showing further 
development of neck and enlargement of central cell preparatory to forming the axial 
row ; c, neck further developed and axial row complete (binucleate neck canal cell, 
ventral canal cell, and egg); d, mature archegonium, with neck complete, neck canal 
cell disorganized, ventral canal cell breaking down, and egg rounded off. 
of the neck canal cells, a process which is completed when seed plants 
are reached. 
Fertilization. In fertilization the sperm enters the neck of the 
archegonium, ciliated end first; and then the ciliated beak ceases 
to function. As the sperm enters the cytoplasm of the egg, the cyto- 
plasmic sheath of the sperm, including the beak, is often left behind, 
and the male nucleus moves alone through the egg cytoplasm to the fe- 
male nucleus; but in some cases the whole sperm has been observed 
within the egg nucleus. 
Embryo. In the development of the embryo, the four great body 
regions are said to be differentiated at the quadrant stage; but in passing 
from Marattiaceae to Polypodiaceae the quadrants are directed dif- 
ferently. Among Marattiaceae the first division of the egg is transverse 
to the long axis of the archegonium (fig. 394), by far the most common 
plane. The current account is that this first division differentiates the 
shoot (stem and leaf) from the foot and root, the former being repre- 
sented by the inner cell, the latter by the outer; and that at the quadrant 
stage the two outer (ventrally directed) quadrants develop the foot and 
