Although our knowledge of the anatomy of _Sigillaria_ has been considerably extended since Williamson[532] drew attention to our comparative ignorance of the subject, there are several points on which information is either lacking or very meagre. As regards the stele, it is in all types so far investigated, of the medullated type and constructed on the same plan as that of _Lepidodendron Wünschianum_, _L. Veltheimianum_, and other species. Secondary xylem was developed at an early stage of growth, and its relation to the primary xylem, from which as Kidston points out in his description of _S. elegans_, it may be separated by a few parenchymatous elements, is like that in _Lepidodendron_. The tendency of the outer face of the secondary xylem to present a crenulate appearance in transverse sections may, as Scott thinks[533], be a feature of some diagnostic importance, but this is not a constant character in the genus. In origin and in their mesarch structure, the leaf-traces closely resemble those of _Lepidodendron_. The earlier account of the structure of the leaf-traces of _Sigillaria_, which were described as possessing both centrifugal and centripetal wood, led Mettenius[534] to draw attention to an important anatomical resemblance between this genus and modern Cycads. This comparison was, however, based on a misconception; the Cycadean leaf-trace, consisting solely of primary wood, is not strictly comparable with those of some species of _Sigillaria_, in which one part of the xylem is primary and another secondary. The occasional presence of secondary xylem in Sigillarian leaf-traces is matched in some _Lepidodendra_[535], and cannot be accepted as a distinguishing feature.