XIV] PLEUEOMEIA 71 



rock. As seen in fig. 134, D, a, the fi:actured surface of a 

 basal area may reveal the existence of an axial vascular cylinder 

 giving off slender branches to the rootlets. 



The bulbous enlargement at the base of the Brown sea- 

 weed Laminaria bulbosa Lam.^ simulates the swollen base of 

 Pleuromeia ; but a confusion between these two plants is hardly 

 likely to occur. Above the Stigmaria-like base the gradually 

 tapered axis, in the less decorticated specimens, bears spirally 

 disposed transversely elongated areas consisting of two tri- 

 angular scars between which is the point of exit of a leaf-trace. 

 The form of the leaf-scars is best seen on the face of a mould 

 figured by Solms-Laubach (fig. 134, C) : in this case the two 

 triangular areas appear as slight projections separated by a 

 narrow groove marking the position of the vascular bundle of 

 the leaf. The curved lines above and below the leaf-scar 

 probably mark the boundary of the leaf-base. The two 

 triangular scars are compared by Solms-Laubach and by 

 Potonie with the parichnos-scars of Sigillaria and Lepido- 

 dendron (c£ fig. 146, C), but the large size of the Pleuromeia 

 scars constitutes an obvious difference though possibly not a 

 distinction of importance. 



The occurrence of a vertical canal filled with carbonaceous 

 material in some of the stems throws light on the internal 

 structure : the canal, which is described by Solms-Laubach as 

 having a stellate outline in transverse section recalls the narrow 

 central cylinder of a Lepidodendron stem, and this comparison 

 is strengthened by the presence of obliquely ascending grooves 

 which represent leaf-traces passing through the cortex. In 

 specimens which have lost more of the cortical tissues the 

 surface is characterised by spirally disposed, discontinuous 

 vertical grooves representing portions of leaf-traces precisely as 

 they appear in similar casts of Lepidodendron. There is no 

 direct evidence of the existence of secondary wood in the stem, 

 but, as Potonie has pointed out, the greater transverse elongation 

 of the leaf-scars in the lower part of a cast (fig. 134, A) points 

 to the production of some secondary tissue either in the 

 vascular cylinder or cortex, or possibly in both regions. 

 J Barber (89) Pis. v. vi. 



