We have no proof of the nature of the subterranean organs of _Lepidodendron fuliginosum_, though it is not improbable that the specimens described below may be correctly assigned by Weiss to that species. Prof. Weiss[335] has made an interesting contribution to our knowledge of a type first described by Hick[336] under the name _Tylophora radiculosa_, a designation which he afterwards altered to _Xenophyton radiculosum_[337] and for which we may now substitute _Stigmaria radiculosa_ (Hick). Prof. Williamson expressed the opinion that _Xenophyton_ exhibited considerable affinity with _Stigmaria ficoides_ and Weiss’s further study of the species leads him to regard Hick’s plant as probably the Stigmarian organ of _Lepidodendron fuliginosum_. The diagrammatic transverse section represented in fig. 177, A (4·5 cm. in diameter), shows an outer cortex of parenchyma, _c_³, consisting in part of radial rows of secondary tissue and of a band of compact parenchyma bounded by the wavy line _a_; at _sc_ is a series of secretory strands exactly like those in a corresponding position in _Lepidodendron fuliginosum_ and other species of the genus. The greater part of the organ is occupied by a lacunar and hyphal middle cortex identical in structure with that shown in fig. 178, B, drawn from a rootlet. At _d_, fig. 177, A, the middle cortex has been invaded by a narrow tongue of outer cortical tissue. The stele is characterised by a large pith filled with parenchyma; in _Stigmaria ficoides_[338] the general absence of pith-tissue has led to the inference that the stele was hollow. The xylem is represented by a ring of bundles separated by broad medullary rays; each bundle contains a few small, apparently primary, elements on its inner edge but is mainly composed of radial rows of secondary tracheae _x_², fig. 177, B. On the outer face of the secondary xylem occur a few smaller and thinner walled cells, _c_, having the appearance of meristematic tissue; from these additional tracheae were added to the xylem. This meristematic zone occurs, as in the stems of _Lepidodendron_, immediately internal to the secretory tissue, sc; at _c_¹, fig. 177, B, is seen the inner cortical tissue. [Illustration: FIG. 178. _Rootlet of Stigmaria._ (From a section in the Manchester Collection.)]