70 REVUE BRYOLOGIQUE 
the ventral half of a lateral segment; in the Microlepidozia type, 
the dorsal half of a lateral segment ; in the Acromastligum type, on 
of the halves of a ventral segment; in the Radula type, a portion 
only of the ventral half of a lateral segment. 
In the Frullania, Microlepidozia and Acromasligum types the 
braneh is always accompanied by an incomplet leaf, which repre- 
sents the other half of the same segment; in the Radula type 
the branch is accompanied by a complete leaf, which belongs to 
the same segment. 
In the Frullania type the first branch-segment is ventral, and 
usually gives rise to an underleaf, the second segment is acrosco- 
pic (with respect to the branching axis) and gives rise to the first 
_ lateral leaf, while the third segment gives rise to the second late- 
ral leaf, basiscopic in position. The branch-spiral in homodro- 
mous with the axis when the branch has arisen in an anodic seg- 
ment-half, and antidromous when it has arisen in a kathodie 
segment-leaf. . 
In the Microlepidozia type the third branch-segment is ventral 
in position, and the branch-spiral is always homodromous with 
the axis because the branches of this type always arise in anodic 
segment-halves. 
In the Acromastigum type the third branch-segment is ventral 
(just as in the Microlepidozia type),and the branch-spiral is homo- 
dromous or antidromous with the axis, according to whether the, 
branch is situated in the anodic or the kathodie segment-half. 
In the Radula type the first branch-segment is sometimes ven- 
_tral, but usually lateral and basiscopic. The branch-shiral is 
usually sinistrorse on the left-hand side of à branching axis, and 
aextrorse on the right-hand side (when the shoot is viewed from 
‘the ventral surface), but subfloral innovations in the Lejeuneæ 
sometimes show variations. 
The leaves at the base of a terminal branch, especially one of 
the Frullania type, are more or less modified in form, in size, and 
in manner of attachement, some of these modifications represen- 
ting reversionary tendencies and other special adaptations. 
Intercalary hranches may be either lateral or ventral in posi- 
tion. Their spirals show little or no relation to the spiral of the 
branching axis, and there is nothing definite about the position of 
_ the first branch-segment. The modifications at the base of a 
branch are reversionary in character. 
There is some evidence (derived from phylogenetie and onto- 
. genetic considerations) that the Frullania type of branching was 
the first one to make its appearance, that this was followed by 
