3i 
Evans . — Branching in the Leafy Hepaticae . 
example, such as Riccardia (. Aneura ) and Pellia^ he considered the terminal 
branching to be essentially the same as that of the Frullania type ; in more 
advanced genera, such as Hymenophyton ( Umhraculum ) and Symphyogyna , 
he distinguished terminal branches of both the Frullania and the Radula 
types ; while in the ventral sexual branches of Metzgeria and Hy7nenophyton 
he found typical intercalary branches comparable with those of Lepidozia 
and Cephalozia. In the Metzgeriaceae, therefore, there is at least a vague 
indication that the types of branches which he regarded as the more 
recent are associated with genera which show other advanced characteristics. 
If it is assumed that the Jungermanniaceae are descended from some 
thallose member of the Metzgeriaceae, it would be natural to conclude that 
the various types of branches were among the characteristics directly 
inherited. The probability of a polyphyletic origin of the J ungermanniaceae 
must, however, be kept in mind, especially in view of the fact that the leafy 
genera of the Metzgeriaceae are doubtless descended from more than one 
thallose ancestor. There is some evidence, for example, that the Jubuloideae 
(of Schiffner) are descended from the Metzgerioideae, while the Epigoni- 
antheae came from such genera as Pellia and its allies. If this is the case 
it is of course possible that some of the primitive Jungermanniaceae came 
from thallose ancestors showing only one or two of the types of branching 
characteristic of the Metzgeriaceae as a whole. The result would be that 
the lines of development commenced by such primitive forms would either 
lack the types of branches which they failed to inherit or would acquire 
them independently. Probably both courses were pursued by different 
evolutionary lines. If it is admitted, therefore, that the branches appeared 
in the sequence indicated by Leitgeb, it must also be admitted that this 
sequence may have appeared in various distinct phyla. 
Aside from the unsatisfactory phylogenetic evidence just brought 
forward, there is also ontogenetic evidence supporting Leitgeb’s ideas of 
sequence. In a species where several types of branching are present it 
will be found that terminal branching tends to appear first in the life-history 
of an individual plant, and that branches of the Frullania type tend to come 
before those of the Radula type. This is well illustrated by both the 
Jungermanniaceae and the Metzgeriaceae. In Lepidozia and Metzgeria , 
for example, the terminal vegetative branches precede the sexual intercalary 
branches, while in Bryopteris the vegetative branches of the Frullania type 
precede the sexual and flagelliform branches of the Radula type. 
Leitgeb concluded further that the various types of branches were 
genetically related to one another. He considered that the Radula type 
was derived from the Frullania type through a delay in the process of 
branch formation, and that intercalary branches represented the culmination 
of this tendency to delay. Even if the importance of such a tendency as an 
evolutionary factor is recognized, it is difficult to understand how one type 
