5 
Evans . — Branching in the Leafy Hepaticae. 
latter near its ventral extremity ; the second wall extends from this first 
wall to the division wall, lying approximately parallel with the acroscopic 
wall; the third wall connects the first two walls. This sequence is the 
same in both segments, although segment i is situated on the right-hand 
side of the apical cell and segment % on the left-hand side, a difference 
which brings the branch in segment i in the kathodic segment-half and 
that in segment 2 in the anodic half. As Leitgeb points out further, this 
will make the spiral of the branch on the left-hand side sinistrorse, and 
therefore homodromous with that of the branching axis, while the branch 
on the right will be dextrorse and antidromous. If the branching axis 
were dextrorse the left-hand branch would still be sinistrorse and therefore 
antidromous, while the right-hand branch would be dextrorse and homo- 
dromous. In other words, the branches which arise in the anodic segment- 
halves are homodromous with the branching 
axis, those arising in the kathodic halves 
being antidromous. 
Of course the relationships which have 
just been brought out remain equally evident 
after the axis and its branches have developed 
further, and it is usually quite possible, from 
the study of an older shoot, to recognize the 
Frullania type of branching at a glance and 
to refer the various appendages of the branch 
to their appropriate segments. As might 
naturally be expected, the first cell cut off 
from the segment-half gives rise to the first 
underleaf of the branch, the second cell to the 
first lateral leaf (always situated on the side of the branch turned towards 
the apex of the branching axis), the third cell to the second lateral leaf (on 
the opposite side), the fourth cell to the second underleaf, and so on. With 
regard to the spirals', the branches on the left-hand side (when the shoot 
is viewed from the ventral surface) will all be sinistrorse and those on the 
right-hand side will all be dextrorse, whatever may be the direction of the 
spiral in the branching axis. 
On account of the fact that a branch represents an entire ventral 
segment-half, only the dorsal half is left to form the leaf adjacent to the 
branch. This leaf consequently differs more or less from normal leaves, 
the most important differences being in form and in the number of lobes 
present. Sometimes, however, the leaf shows interesting peculiarities in 
its method of attachment. The leaves and underleaves at the base of 
a branch are also subject to more or less modification, both in form and in 
position. The differences in position are largely due to the fact that the 
first segments cut off from the original segment-half are less definitely 
Fig. 5. Diagram representing 
the establishment of two branches 
of the Frullania type. 
