Branching in the Leafy Hepaticae. 
BY 
ALEXANDER W. EVANS, 
Professor of Botany in Yale University. 
With thirty-six Figures in the Text. 
HE branching of the shoot in the Hepaticae was carefully studied by 
i Leitgeb (’71 tf, ’71 b, ’72, ’75) about forty years ago. Although most 
of the previous writers on this subject had confined their attention to a few 
thalloid genera, Leitgeb extended his observations to include a large number 
of leafy forms. He was able to demonstrate the fact that throughout the 
Jungermanniales (comprising the Metzgeriaceae and the jungermanniaceae 
of many recent writers) the branches are never formed by a true dichotomy ; 
that, in other words, the apical cell of a branching shoot never gives rise by 
a median longitudinal wall to the apical cells of two branches, a process 
which takes place in certain dichotomous Algae, such as Dictyota. In the 
Jungermanniales the branches invariably arise in segments cut off from the 
apical cell, and it is the persistence of the latter in the branching axis which 
indicates that the branching is monopodial in character. 
Leitgeb showed further, however, that the apical cell of a future branch 
often made its appearance in an exceedingly young segment. Under these 
circumstances, if the branch grows vigorously and deflects the main axis to 
one side, the branch-system may simulate a dichotomy very closely. This 
is the case, for example, in Metzgeria furcata and in the genus Bazzania 
(Fig. 27). If, on the other hand, the branch grows less vigorously than the 
main axis and assumes a distinctly lateral position the branching is obviously 
of the monopodial type. Riccardia multifida and Lepidozia reptans (Fig. 8) 
may be cited as examples of this condition. When the branches arise close 
to the apical cell, as in the cases just considered, Leitgeb distinguishes the 
process as ‘ Endverzweigung ’ or ‘ Terminal Branching’. He contrasts with 
this * Intercalary Branching ’, in which the branches first appear at some 
distance from the apical cell. In this latter type of branching the monopodial 
character is always apparent. It should be noted also that segments in 
which terminal branches begin their development are embryonic in character 
and are still undergoing cell-divisions ; those where intercalary branches 
arise, on the other hand, have become more or less completely differentiated., 
and their cells have apparently ceased dividing. 
[Annals of Botany, Vol. XXVI. No. Cl. January, 1912 ] 
B 
