2 Evans. —Branching in the Leafy Hepaticae. 
Although Leitgeb’s distinctions are based on differences in develop- 
ment, the two types of branches can usually be recognized in mature plants 
on account of the fact that terminal branches arise exogenously while inter- 
calary branches arise endogenously. The result is that the superficial tissues 
of a terminal branch are continuous with those of the axis, while an inter- 
calary branch shows a distinct sheath at its base formed by ruptured cortical 
tissues. In the present paper the branching in the Jungermanniaceae will 
alone be considered. This group, which is the equivalent of the Junger- 
manniae akrogynae of certain writers, includes the vast majority of the leafy 
genera and illustrates both terminal and intercalary branching much more 
fully than the other groups of the Hepaticae. 
In order to give a clear idea of the way in which branches arise it will 
be necessary to describe briefly the normal divisions which take place in 
young segments. Here again our knowledge is largely based upon the 
work of Leitgeb. With the exception of the genus Pleurozia , where Goebel 
Figs, i and 2. Diagrams representing the sequence of segments cut off from apical cells. 
Fig. 1. Spiral dextrorse. Fig. 2. Spiral sinistrorse. 
(’ 93 , p. 453) has demonstrated a two-sided apical cell, the Jungermanniaceae 
all grow by means of a tetrahedral apical cell, which cuts off three longitu- 
dinal rows of segments in the usual way. On account of the orientation of 
the shoot one row of these segments will occupy a ventral position and the 
other two lateral positions (Fig. 1). When the segments are first cut off 
they are approximately in the form of flat triangular prisms, each bounded 
by two broad faces or walls and three narrow walls. One of the broad 
faces will lie in contact with the apical cell and may, as Leitgeb suggests, 
be designated the acroscopic wall ; the other broad face, lying in contact 
with the next older segment of the same row, may then be distinguished as 
the basiscopic wall. Of the three narrow faces one, the free wall, will be 
exposed at the apex of the shoot, while the two others will come into 
contact with segments of the two other rows. In the lateral segments these 
two narrow faces may be distinguished as the dorsal and ventral walls 
respectively. They may be distinguished also according to the direction 
of the spiral in which the leaves are arranged. In Fig. 1, for example, which 
represents a dextrorse spiral, the dorsal wall in segment 4 is kathodic and 
the ventral wall anodic ; in segment 3, on the other hand, the dorsal wall 
