256 Campbell.— -On the development 
divisions in the leaf-octant are less regular, and very often the 
apical cell becomes obliterated at an early period (PI. XIV, 
Fig. 1 6 c). 
There seems to be no rule as to which of the octants of 
the stem-quadrant forms the apical cell of the stem, as it 
was found in about an equal number of cases to be right or 
left. The succession of segments cut off from the apical cell 
proceeds from the outside towards the octant -wall, the 
three segments of each series being respectively approximately 
parallel to the quadrant-, basal, and octant- walls. The 
direction of the leaf-spiral, which depends upon the arrange- 
ment of the segments, will of course be determined by the 
position of the original stem-octant with reference to the octant- 
wall. Kny 1 comes to similar conclusions with reference to the 
establishment of the leaf-spiral in Ceratopteris. 
Each segment divides by a tangential wall into an inner and 
outer cell, the former dividing again by a similar wall and the 
latter by a radial wall, so that a vertical section through the 
young segment at this stage (PI. XIV, Fig. 18) shows four cells, 
two inner and two outer ones. The inner cells undergo re- 
peated division in all directions, but the outer ones only by 
radial walls. 
The stem grows very slowly at first, and by the time the first 
leaf and root have attained length enough to break through 
the prothallium, the stem shows only about two completed 
series of segments. Even at this stage (PI. XIV. Fig. 23) the 
inner cells of the segments have rapidly divided and the first 
traces of the vascular bundle are distinguishable. 
The first segments are larger than the succeeding ones, and 
the broadly tetrahedral form of the original octant is thus 
rapidly reduced to the much narrower form of the apical cell 
of the older stem. 
The octant which does not become the apical cell of the 
stem, forms, as we have seen, the second leaf of the plant. In 
a certain sense, assuming that the quadrant-wall establishes 
1 Kny, Die Entwicklung der Parkeriaceen, in Nova Acta Acad. Leopold, xxxvii, 
No. 4, p. 58. 
