650 DR R, KIDSTON AND PROF. W. H. LANG ON OLD RED SANDSTONE PLANTS 
differences in size are best explained by the fragments coming from different 
positions in a branch-system. Along with the difference in size there is naturally 
some in the details of the structure, but a common plan of construction holds 
throughout. This will be evident in comparing the specimens figured on 
Pis. VI and VII. 
Since the shoots in the material examined are represented by short fragments, 
no general picture of the branch-system can be obtained. Examples of the 
branching, which in most cases was lateral, will be described later. 
The stem bore numerous leaves of relatively small size, so that the general form 
of the plant must have depended on the branching. The first leaves on the 
transition region from the rhizome have been seen to be small scales (figs. 18, 19, 23, 
and 95), sometimes without any leaf- traces in connection with them, and at other 
times with a small trace extending to the base of the leaf. The leaves on the 
aerial shoots are larger, but their leaf-traces also never extend into the free portions, 
ending in the enlarged leaf-bases (fig. 35). The long simple leaves are seen attached 
to the stem in the longitudinal sections represented in figs. 31 and 32. They are 
met with cut across, around many of the transverse sections of stems (figs. 96 
and 46). These and other sections also show the projecting leaf-bases, while in 
fig. 33 the leaves are just separating from the stem. While the leaf-bases on the 
stem include the ends of the leaf-traces, the sections of the free portions of the leaves 
have never shown any indication of the presence of a vascular bundle, however 
well preserved the tissues may be (cf. figs. 96 and 37). Fig. 36 shows the leaves 
closely crowded, and so arranged as to suggest that the section has passed across a 
bud. On the stems the leaves were more or less closely placed, and, as the arrange- 
ment of the leaf-traces shows, were borne spirally. A leaf lying free in the matrix 
is shown in fig. 38, while others are cut so as to show the stomata in fig. 40. Fig. 30 
is a cross section of a very small twig, with the closely placed leaves around it. 
In cross section the leaves were oval, being thus slightly dorsiventral. 
The arrangement of the tissues in the stem is most clearly brought out in 
transverse section. A survey of the figures on Pis. VI, VII, and XIII will show 
the features mentioned in the followingfgeneral description, which is based on the 
better-preserved examples of large or medium size. 
The surface of the stem and leaf-bases is bounded by an epidermis (ep.). This 
has a well-marked cuticle, which is often traceable as the limit of the stem when the 
epidermal cells are unrecognisable. Within the epidermis is a narrow zone of outer 
cortex ( o.c .). The inner cortex ( i.c .) is sometimes uniform, but is usually differentiated 
into outer, middle, and inner zones ( i.c.o ., i.c.m., i.c.i.). Only in the case of one 
stem has an endodermis-like layer ( en .) been recognisable limiting the stele, which 
in all cases, however, is clearly contrasted with the cortex. The arrangement of the 
tissues in the stele has already been traced in the more advanced specimens of the 
transition region. The xylem ( xy .) is stellate in cross section, and groups of 
