4 Evans . — Branching in the Leafy Hepaticae. 
lobes one or both of the external cells of the young segment divide before 
the development of the leaf is clearly begun, and in this way the extra 
lobes are provided for. In the development of a leaf the segment-halves 
project and become divided by periclinal walls; these cut off the rudiment 
of the leaf from the cells which, by their further divisions, will form the 
cortical tissues of the stem. In ventral segments where underleaves are 
formed the development proceeds in much the same way. 
Terminal Branching. 
According to Leitgeb (’71 b) terminal branches always arise in the 
ventral portions of the lateral segments. He recognizes, however, two 
distinct kinds of terminal branching. In the first, which he describes as 
branching from a segment-half, the branch represents the entire ventral 
half of a segment, the apical cell of the branch making its appearance before 
the walls separating the leaf-rudiment from the cortical cells have been laid 
down. For the sake of convenience this may be designated the ‘ Frullania 
type’ of branching. In the second kind, which he describes as branching 
from the basiscopic basilar portion of a segment, the apical cell of the 
branch arises in a cortical cell of the axis after the leaf-rudiment has been 
cut off. The branch represents therefore a much smaller portion of the 
segment than a branch of the first kind. Branching of the second kind may 
be distinguished as the ‘ Radula type ’. 
About ten years ago the writer discovered in the Hawaiian genus 
Acromastigum (’00) a third kind of terminal branching, in which the branch 
represents a half of one of the ventral segments. No other representatives 
of this kind of branching have been discovered and it may be called the 
* Acromastigum type’, although other kinds of branching occur in the same 
genus. A fourth kind of terminal branching, in which the branch represents 
the dorsal half of a lateral segment, is described below. It is known only 
in the subgenus Microlepidozia of the genus Lepidozia , and may therefore 
be characterized as the ‘ Microlepidozia type ’. 
The Frullania Type. 
Leitgeb (VI b) describes the development of branches of this type very 
clearly, and his diagram of a sinistrorse branching axis, which is here repro- 
duced in a slightly modified form (Fig. 5), illustrates the sequence of the 
early divisions. In segments 1 and 2 the ventral halves have each under- 
gone four divisions, which have cut off the tetrahedral apical cells of the 
future branches. In fact each of these segment-halves is essentially an 
apical cell from the beginning, the three cells first cut off acting as the 
first three segments of the branch. It will be noted that the walls in the 
segment-halves are in the following sequence : the first wall extends from 
the first division wall of the segment to the acroscopic wall, meeting the 
