30 Evans . — Branching in the Leafy Hepaticae. 
the Hawaiian B. Brighami , shows a branch of this kind and may be 
considered as representative of ventral intercalary branches in general. 
These branches, as Leitgeb long ago pointed out, are usually situated in 
the axils of underleaves or in corresponding positions in species where 
underleaves are not formed. In the example figured it will be noted that 
the underleaf with the axillary branch is strongly reflexed. 
There seems to be no definite sequence in the leaves of a ventral inter- 
calary branch ; neither is there any apparent relation between the spiral of 
a branch and that of the branching axis. The modifications present are 
similar to those described under lateral branches. Although ventral 
branches of this type usually occur singly in the axils of underleaves, in 
certain genera, such as Calypogeia ( Kantia ), two or three of them are some- 
times found side by side. In other cases, such as Cephalozia bicuspidata , 
a branch may develop from any part of a ventral segment. Sometimes 
branches of this character arise directly from fully differentiated cortical 
cells and are thus destitute of basal sheaths. Such branches are to be regarded 
as adventive rather than as intercalary, although the distinctions between 
the two are not always hard and fast. Adventive branches in this position 
are essentially like those which sometimes spring directly from leaf-cells. 
They represent a type of regenerative process and scarcely come within the 
scope of the present paper. 
Subfloral innovations in Radula , Jubula , and the Lejeuneae have 
already been spoken of in connexion with the Radida type of branching. 
They apparently arise whether fertilization has taken place or not. In 
many plants with intercalary branching subfloral innovations are also found, 
but their development, in certain cases at least, is dependent upon an absence 
of fertilization. Such innovations, which seem to be always intercalary in 
origin, usually occur singly, although groups of from two to four are not 
infrequent in certain species. They arise both in lateral and in ventral 
segments, the latter position being somewhat more common. The innova- 
tions are usually more robust than other intercalary branches, but show no 
further distinctive characteristics. 
General Considerations. 
From his study of the various types of branches in the Jungerman- 
niaceae, Leitgeb (’75, ’77) reached the conclusion that they had made their 
appearance in a definite phylogenetic sequence. He believed that branches 
of the Frullania type came first, that these were followed by branches of 
the Radida type, and that intercalary branches came last. He obtained 
support for these ideas not only from the Jungermanniaceae themselves but 
also from the Metzgeriaceae, the branches of which he homologized with 
those of the Jungermanniaceae. In the more primitive Metzgeriaceae, for 
