102 Proceedings of the Royal Physical Society. 



Fig. 1, a\ a), the larger ones being next to the parenchyma, 

 some of which, in fact, are scattered through it. These vessels 

 become somewhat smaller as they recede from the axis, and 

 on their outer margin are encompassed by a narrow band of 

 very small scalariform vessels, and it is from these last that 

 the foliar bundles are given off (PL II., Figs. 1, 2, and 4, a). 

 They are of similar structure to the larger scalariform tubes, 

 but very much smaller. 



At various points in the circumference of this narrow band 

 aggregations of scalariform vessels occur. These belong to the 

 leaf system, and similar bundles are found in all parts of the 

 stem, from this region out to the periphery (PL II., Fig. 2, i). 



The vascular system in this plant I look upon as represented 

 by the central cylinder of intermingled vessels and parenchyma, 

 what may be viewed as a single central vascular bundle, from 

 which small twigs pass outwards and upwards to the leaf 

 bases (PL II., Figs. 1 and 2, a, and PL Il.a, Fig. 2, a). 



I cannot trace any indication of ligneous zone or medullary 

 rays, either in this species or in any other Lepidodendron I 

 have examined. 



It would appear that the system of small scalariform 

 vessels, which surrounds the circumference of the central 

 bundle, has been taken for a ligneous zone by Professor 

 Williamson — a view which seems untenable, if I am correct 

 in connecting this part with what he terms the ligneous zone. 



This vascular system is invested by a delicate cellular 

 envelope, which seems to have very seldom resisted decay, 

 before mineralisation took place. A few traces of it are left 

 in this specimen, sufficient to indicate its nature (PL II., 

 Figs. 1 and 2, h). 



Each of the foliar bundles was encased in a sheath of this 

 tissue, which filled up the large openings in the bark, through 

 which they passed to the leaves.* 



I have seen this parenchyma well preserved in Lepidodendron 

 Harcourtii, where it was sharply defined by its more deUcate 

 structure (PL IL, Fig. 5, c) from the adjoining outer layer. 



This delicate parenchyma has been designated the inner 



* It is not preserved in the specimen now described, but was well shown in 

 Lep. Harcourtii, from which Fig. 5 was drawn. 



