648 DR R. KIDSTON AND PROF. W. H. LANG ON OLD RED SANDSTONE PLANTS 
while retaining the simple contrast of a narrow outer and a broad inner zone, 
often appears more definite and better preserved. The central xylem becomes 
stellate in cross section, thus intruding into the wide zone of phloem. Scale- 
leaves appear on the surface. These sometimes have leaf-traces in relation to them, 
but may be borne on a region of the stem with no leaf-traces. 
The general features will be evident from the specimens represented in figs. 15-25 
and fig. 95. Some of these examples will now be referred to and described. 
In the portion of clear peat included by fig. 15 there are to be seen a 
rhizome of medium size cut in obliquely longitudinal section, and below this 
a transverse section of an axis with the characters of the transition region. The 
general correspondence in structure between them will be evident at a glance. 
The- xylem strand of the transition region is damaged, but is surrounded by a 
broad zone of phloem, and is not giving off any leaf-traces, and none are present 
in the cortex. This is differentiated into a broad inner cortex and a narrow zone 
of outer cortex. The epidermis has broken down around part of the circumference, 
but is very distinct on the other part. Here the outline is irregular, owing to 
projections which comparison with other specimens shows to be scale-leaves. A 
small intrusive rhizome is to be seen in the cortex on the lower side of the figure. 
The longitudinal section shown in fig. 16 has also essentially the same structure 
as the rhizome, and may be compared with fig. 6. It differs in the strongly 
developed epidermis and cuticle, the indications of scale-leaves (sc. 1.), and the 
presence of a few leaf-traces, one of which is shown at the lower part of the figure 
at l.t. The cortex, which is rather broken down, shows outer and inner zones. 
The stele is of the type characteristic of the rhizome, with a broad zone of 
exceptionally well-preserved phloem (cf. fig. 22) around the large but simple 
strand of xylem. 
The two axes, still connected as they have arisen by branching, in fig. 25 show 
a similarly simple structure in transverse section, while the smaller axis above 
is in a more advanced stage of transition, with an angled xylem giving off leaf- 
traces. 
Successive stages of the transition from different specimens are seen in figs. 17, 
18, 19, and 24. The specimen in fig. 17 hardly differs from a rhizome, except in 
the distinctness of the epidermis. There are no leaf-traces or indications of scale- 
leaves. The stele of this axis, which is to be regarded as in an early transition 
.stage, has just given off a small lateral branch. The transverse section in fig. 18 
shows the small scale-leaves very well. No leaf-traces are passing out to them, but 
the xylem of the stele is distinctly angled. This is still more marked in the small 
stem in fig. 25, in which a leaf-trace is departing from one angle of the quadrangular 
xylem. The stem represented in fig. 19 is preparing to branch, and contains two 
steles. The xylem of these has projecting rays, which extend nearly to the limit 
between the phloem and inner cortex. This stem bears scale-leaves, and, in relation 
