Professor A. C. Seward—Fossil Plants from South Africa. 485 
formed by a subepidermal tissue ; the scar, which interrupts the con- 
tinuity of the flat surface, may mark the position of a leaf-base, or, 
assuming a partial decortication to have occurred prior to fossilisation, 
the scar may represent a gap in the cortical tissue caused by the decay 
of delicate tissue surrounding the vascular bundle of each leaf in its 
course through the cortex of the stem. Gaps of this nature are 
characteristic features in tangential longitudinal sections through the 
outer cortex of petrified Lepidodendron stems from the English Coal- 
measures. The indication of grooves seen on some of the areas 
(Fig. 6, g, g.) may mark the course of the vascular bundles passing 
‘inwards and downwards through the cortex. If the impression 
(Fig. 6) were that of the actual surface of a Lepidodendron or 
a Sigillaria stem we should expect to find traces of the parichnos 
(a strand of tissue which accompanies the leaf-bundle of these plants 
and forks into two arms just below the base of a leaf) appearing on 
the leaf-scar as two small scars, one on each side of the scar of the 
leaf-bundle. In the specimens from Vereeniging described in 18971 
as Srgillaria Brardi, which bear a superficial resemblance to the 
Elandsdraai fossil, the parichnos is clearly shown. On the other 
hand, an impression of a partially decorticated Lepidodendroid stem 
need not necessarily show the parichnos as a distinct feature: owing 
to its close association with the leaf-trace in the outer cortex; before 
its separation in the form of two diverging arms, it would not appear 
as a distinct gap apart from that representing the leaf-bundle.? The 
absence of the parichnos may be regarded as a point in favour of the 
view that the impression is that of a partially decorticated stem. 
Similarly, the absence of any demarcation between a leaf-cushion and 
a true leaf-scar such as characterises the stems of Lepidodendra and 
many Sigillarie is also favourable to the same interpretation. The 
fact that a partially decorticated stem often presents an appearance 
comparable to that of serially disposed leaf-cushions is in some 
instances due to the presence of a reticulum of thicker-walled elements 
in the outer cortex, which divides up the thinner-walled tissue into 
regular meshes or areas corresponding approximately in shape to the 
leaf-cushions. It may be that the dark band, z, shown in Fig. 7, is 
the impression of some of the fibres composing a reticulum of 
strengthening tissue. It is, however, possible that the cells seen in 
Figs. 7 and 8 may be those of the epidermal layer, and the absence of 
a parichnos may constitute a definite character, but this is on the 
whole less likely than the other hypothesis. Although we cannot 
feel much confidence in the specific determination of stems which 
have probably lost part of their surface features, we may briefly refer 
to other. specimens which bear a close resemblance to the African 
fossil. 
In 1872 Mr. Carruthers* described some Paleeozoic impressions from 
Queensland, some of which appear to be identical with that shown in 
Fig. 6 under the name Lepidodendron nothum, Ung. The material on 
Seward: Quart. Journ. Geol. Soc., vol. liii (1907), p. 326, pl. xxiii. 
For figures of the parichnos strand see Williamson, Phil. Trans. Roy. Soc., 1893. 
Carruthers : Quart. Journ. Geol. Soc., vol. xxvii, 1872. 
on rer 
