72 Campbell. — On the Prothallium and Embryo of 
The Embryo. 
The first division of the fertilized egg is the same, with 
respect to the archegonium, as that of the Polypodiaceae, i. e. 
the basal wall is parallel with the axis of the archegonium ; 
but the second or quadrant wall is also parallel with the 
axis of the archegonium, instead of transverse, as in the other 
Filices, although its position with reference to the prothallium 
is the same ; that is, parallel with its surface. The position 
of the quadrants, therefore, and later the primary organs of 
the embryo developed from them, is the same with reference 
to the prothallium as in the other ferns, but not as regards the 
archegonium. 
The lateral more or less varying position of the arche- 
gonium causes more or less diversity in the direction of 
growth in the primary organs of the embryo, and a cor- 
responding difficulty in orienting the prothallia in making 
sections. The results given here were obtained from a com- 
parative study of a large number of series of sections, cut in 
three directions — longitudinal, horizontal, and transverse. 
The primary organs — stem, leaf, root, and foot — are estab- 
lished as soon as the two first walls are formed in the young 
embryo. These walls, lying at right angles to each other, 
divide the embryo into four nearly equal cells, two epibasal 
and two hypobasal, i.e. two turned toward the front of the 
prothallium, and the others toward the back. In each 
of these cells are next formed the octant-walls (Fig. 81), and 
the embryo now consists of eight tetrahedral cells, as in other 
ferns, and, as is probably the case in all of these, one of each 
pair of octant cells becomes the apical cell of the organ 
arising from the quadrant. In the foot-quadrant, it is true, 
the divisions are quite irregular, but even here, the first 
divisions correspond to those in the other quadrants, although 
very early all trace of an apical cell is lost. In all the organs 
there is considerably less regularity than obtains in the true 
leptosporangiates, both in regard to the position of the earlier 
walls and in the subsequent differentiation of the tissues. 
