26 
Evans. — Branching in the Leafy Hepaticae . 
In the vegetative branches the differences noted in the innovations do 
not seem to occur. In a large series examined the spirals were all found 
to agree with those in Radula. It may be stated, therefore, that in the 
Radnla type of branching the spirals usually run in the same direction 
as in the Frullania type, dextrorse branches being on the right-hand side of 
a branching axis and sinistrorse branches on the left-hand side. In the 
Radtda type, however, the first underleaf (or first ventral segment) comes 
second in the sequence instead of first. 
Although the branches in Radtda and the innovations in the Lejeuneae 
are clearly exogenous, the exogenous nature of the vegetative branches in 
the Lejeuneae is less apparent, each branch bearing at its base a sheath 
which seems at first sight to be composed of ruptured cortical tissue. The 
common Lejennea cavifolia, of Europe, Asia, and North America (Fig. 33), 
may be chosen to illustrate the conditions present. 
According to Leitgeb ( 75 , p. 28) this sheath is 
really composed of the first leaf-cycle of the 
branch, the first underleaf and the first two lateral 
leaves having coalesced by their margins. The 
leaves are very rudimentary and form at first 
a covering through which the developing branch 
must push its way. In favourable cases he was 
able to demonstrate the boundaries between the 
leaves. He associates these foliar sheaths with 
/»/m FlG Hull'goff f (Finis 4 re)’ the fact that the branches in the Lejeuneae, al- 
France (F. Camus), x 40. though laid down near the apex, often remain 
latent for a considerable period. 
Leaving the foliar sheaths out of consideration, the first leaves on 
branches of the Radtda type show less definite modifications than in the 
other types of terminal branching. They are usually smaller than normal 
leaves, and their lobules (ventral lobes) are often very rudimentary. The 
first underleaves, also, are sometimes smaller and less complex than those 
afterwards formed. In most cases there is a transition, sometimes very 
gradual, between the basal leaves and the more typical leaves which the 
branch later develops. The modifications present may be looked upon as 
reversions to a more juvenile condition. 
Intercalary Branching. 
Terminal branching of the Radula type, as Leitgeb intimates, is inter- 
mediate in certain respects between terminal branching of the Frullania 
type and intercalary branching. In the Frullania type (and the same thing 
is true of the Microlepidozia and Acromastigum types) the branches arise 
very close to the apex, their leaves follow a definite sequence, the branch- 
spirals conform to definite rules, and the exogenous origin is perfectly clear. 
