658 DR R. KIDSTON AND PROF. W. H. LANG ON OLD RED SANDSTONE PLANTS 
fig. 92. An interesting feature in connection with the lateral branching is the way- 
in which the branch may remain connected to its main stem by a web-like 
flange of cortical tissue, as is shown by the example in fig. 88. 
The general character of the branch-trace and its size relatively to the leaf- 
trace can be gathered from figs. 83 and 84. No protoxylem elements are dis- 
tinguishable in any of the branch-traces that have been observed. As is more 
clearly shown by fig. 94, the xylem of the trace is surrounded by a zone of 
collapsed phloem. 
A point of some interest is the more or less close parallel between the assumption 
by the branch-trace of the features of the stem-stele and the changes in the 
transition from the rhizome to the leafy shoot. In the examples of lateral 
branching figured the change is effected rapidly. A specimen has been met with, 
however, in which a branch on a leafy shoot maintained for more than a centimetre 
a broad, clear zone of phloem around the cylindrical strand of xylem of its stele. 
The base of another branch cut transversely in the tangential section of its parent 
stem is shown in fig. 93. The structure of the branch at this level resembles that 
of a rhizome, but soon passed, as succeeding sections of the series showed, into that 
characteristic of the transition region. This section at first suggested the lateral 
origin of a rhizome from a leafy shoot, but cannot by itself be taken as affording 
evidence of this. 
A special account must be given of one case of branching which is remarkable for 
its being apparently endogenous. The large stem exhibiting it has already been 
referred to as the only specimen showing a well-marked layer in the position of an 
endodermis (p. 654); it occurred in the block containing the sporangia, to be 
described below. The stem can be traced unbranched through, a number of sections 
of the series cut from this block. An enlargement of one arm of the xylem and a 
bulging out of the endodermis indicates the approach to the place of branching 
(fig. 97). As the large branch-trace separates and moves outwards it becomes evident 
that the cortex of the branch is continuous with the tissue within the endodermis of 
the main stem (fig. 98, and more highly magnified in fig. 100). This amounts to saying 
that the branch is endogenous. This conclusion is supported by the discontinuity 
between the superficial tissues of the main stem and the branch (fig. 100, X, 
and fig. 101 ). Such a type of branching of the shoot is, so far as we know, unique, 
both among living and extinct Vascular Cryptogams. 
The cortex of this branch is continuous with that of two small stems, which in 
the lower sections of the series lay in the neighbourhood of the large stem. The 
whole series is consistent with the giving off of. an endogenous lateral branch that 
bent back and divided equally. In the higher section figured in fig. 99 the. stele of 
the curved branch is cut through twice, first at hr. tr., where the branch is emerging 
from the main stem, and again where it has divided into two steles within the one 
cortex \Ba, Bb ) at a distance from this. In the section at a lower level (fig. 98) 
