We cannot, in the absence of petrified material, arrive at any satisfactory conclusion as to the meaning of these surface-features. White considers that _Omphalophloios_ is probably a rhizome of one of the arborescent Lycopods, but whether or not this is its true nature must be left for future discoveries. The fact that the rootlet bundles of some Stigmarian axes are accompanied by a parichnos strand, as Weiss has shown, may prepare us for the discovery of surface-features on _Stigmariae_ not unlike those of _Omphalophloios_. (Fig. 193, C.) A possible comparison may be suggested also with _Sigillaria Brardi_ as figured by Germar (fig. 196, A) in which circular scars, which may be the scars of rootlets, occur below the leaf-base areas. It is not impossible that in the surface-features of _Omphalophloios_ we have both leaf and rootlet scars represented. _General considerations._ The solid xylem core characteristic of the stele of some species of Palaeozoic Lycopodiales (e.g. _Lepidodendron esnostense_ and _L. rhodumnense_) may probably, as Tansley and Chick[653] point out, be regarded as the lineal descendant of a primitive axial strand of water-conducting elements. In the course of evolution the centre of the tracheal column became partially converted into parenchymatous tissue, as in _Lepidodendron vasculare_. The arrangement of the short cells in regular vertical series is reminiscent of an early stage in the development of tracheae: instead of forming tubular conducting elements the central part of the stelar meristem acquired the short-celled form; some of the cells became lignified as isodiametric storage tracheae while others persisted as thin-walled parenchyma.