94 BOTANICAL GAZETTE [JANUARY 
When the sporophyte has attained the stage immediately 
preceding the invasion of the gametophytic tissue by the develop- 
ing foot, the first isolation of cells which will contribute definitely 
to the apical group may sometimes be observed (fig. 5). The first 
isolation is suggested by the appearance of more pronounced cell 
walls. In the structure of the cells themselves at this stage there 
is usually no observable difference; but when once the foot estab- 
lishes itself, and the sporogenous cells rapidly increase in density 
and begin elongation, these become more prominent because of 
‘ their less density, their more conspicuous nuclei, and their failure 
to undergo elongation. 
In most cases a single layer of cells is formed, cut off at this 
early stage, although occasionally two layers in addition to the wall 
cells will be found. These originally isolated cells are commonly 
carried forward at the apex as the sporogenous cells below them 
continue their elongation; and they generally compose all there is 
of sterile tissue here, but not uncommonly the amount is increased 
in one of two ways. The sporogenous initials may by periclinal 
divisions contribute to the mass just before the rapid series of anti- 
clinal divisions which accompanies the broadening of the capsule 
and elongation of the sporogenous cells (fig. 7). Moreover, the 
bulk of sterile tissue may be increased by the division of wall cells 
near the apex (fig. 6). The contribution by this method is appar- 
ently very slight and less common than by the former. A third 
method by which the tissue may be increased in bulk would be by 
continued division of the sterile cells after their first isolation. 
Although this would seem a very probable occurrence, I was unable 
to observe any direct evidence of it. The apical end of a more 
mature sporophyte is shown in fig. 8. The sporogenous cells are 
in the tetrad condition, and the close association of the elaters 
with the sterile cap toward which they converge is very 
conspicuous. 
Conclusions 
In the Marchantiaceae, the first family of the Bryophytes in 
which there occurs any sterilization of potentially sporogenous 
tissues, the elaters are commonly diffusely arranged; but in 
