The name _Lepidodendron fuliginosum_ was proposed by Williamson in 1887 for petrified stems previously included by him in Witham’s species _L. Harcourtii_, but subsequently recognised as a distinct type characterised by “the greater uniformity in the composition of the entire cortex” and by other features some of which do not constitute distinctive characters. The species agrees with _L. Harcourtii_ and with _L. Veltheimianum_ in having a medullated stele; it is distinguished not only by the more frequent preservation of the middle cortex, a fact due to a difference in minute structure, but chiefly by the peculiar structure of the secondary tissue added to the stele; this is in part composed of radial series of parenchymatous cells and of a varying amount of tracheal tissue the elements of which are narrower than in other species and are characterised also by their sinuous vertical course. As is pointed out in the sequel, the anatomical features of _L. fuliginosum_, as at present understood, are not confined to one type of _Lepidodendron_ stem. Specimens have been described with leaf-cushions of the form characteristic of _L. aculeatum_, _L. obovatum_ and _Lepidophloios_ combined with the anatomical features of Williamson’s species: it is possible that the two species _L. obovatum_ and _L. aculeatum_ are not really distinct[323], but it is certain that shoots with both the _Lepidodendron_ and _Lepidophloios_ cushions may have the same type of anatomical structure. A more detailed knowledge of the structural features of Lepidodendron shoots may enable us to define anatomical species with more exactness than is possible at present. There can, however, be little doubt that well-marked anatomical features may be associated with more than one specific form of shoot as defined by the form of the leaf-cushions. Solms-Laubach proposed the name _Lepidodendron Williamsoni_ for the anatomical type _L. fuliginosum_ of Williamson, but the latter name has been generally adopted. In the following account special attention is directed to the nature and origin of the secondary stelar tissue and to the secretory zone, as difference of opinion exists as to the interpretation of these features. Among the best examples of shoots of _Lepidodendron fuliginosum_ without secondary tissue or in which it is feebly developed are those originally described by Binney. The stele includes a large parenchymatous pith, the cells of which frequently show signs of recent division, a feature observed also in the pith of the large stem of _L. Wünschianum_, represented in figs. 181, 182. The primary xylem cylinder has an irregularly crenulate outer edge like that of _L. Wünschianum_ and _L. Harcourtii_ and the protoxylem elements occupy an exarch position. Isodiametric reticulately-pitted elements are met with both on the inner and outer edge of the xylem.