1898-99.] © Report of the Bryological Section. 63 
the cell becomes pear-shaped, and three cell walls are then 
formed (fig. 4), intersecting one another at such an angle that 
they enclose a mass shaped like an inverted pyramid (fig. 5). 
This stage brings us to the foundation of the stem with its 
lateral appendages. 
The development of the stem proceeds as follows: A cell 
wall is formed parallel to one of the three faces of the 
pyramidal mass, or apical cell, and cuts off a segment (fig. 6). 
The apical cell is of course reduced in size by this, but begins 
to grow again till it regains its former size (fig. 7), when a 
segment is cut off from the second face (fig. 8). Growth 
again proceeds till the former size is regained, and a segment 
is cut off from the third face of the apical cell. Growth 
and segmentation alternate regularly, and it will be observed 
that the fourth segment is above the first, the fifth above the 
second, the sixth above the third, the seventh above the first 
and fourth, and so on—jin short, it will be seen that the 
segments are ranged in a spiral. When once this is grasped, 
the spiral arrangement of the leaves, which are developments 
of the segments, will be clearly seen. 
Leaving the main stem and observing the segments, we find 
changes have been taking place, but as this is uniform in 
all, we will take one segment and follow it out. A wall is 
formed dividing the segment into an inner and an outer half 
(fig. 9). The inner half goes towards forming the meristem. 
The outer half is divided into a lower and an upper cell (fig. 
10). The lower cell goes to form the cortex. The upper cell 
is divided into two cells by a cell wall (fig. 11). The upper of 
these, by further growth and cell division, develops into a leaf 
(figs. 12 and 13), while the lower may form a branch, and 
this explains why branches are never axillary to the leaves. 
The development of the leaf from the leaf cell takes place 
by segmentation arising from the formation of cell walls 
perpendicular to the surface, and inclined to the right and left 
(fig. 14). The growth is at first apical, but it is limited, and 
when that ceases the leaf grows from the base till it is fully 
developed. The young leaves grow rapidly, and are closely 
imbricated over the growing point, but the elongation of the 
stem eventually separates them. They are always sessile, with 
a broad base inserted into the stem. 
