In _Medullosa stellata_ var. _lignosa_[266] the outer xylem reaches a breadth of 4 cm. and the star-rings are reduced to one. The form _M. stellata_ var. _gigantea_[267] (fig. 416, K) is of special interest as an example of a stem reaching a diameter of nearly 50 cm. and having as many as 43 large and small star-rings in the axial region. A large tubular stele like that of the type-species (fig. 416, D) surrounds the central region, but in this form the cylindrical stele _a_ is succeeded by concentric cylinders of normally orientated xylem and phloem (fig. 416, K, _bb_) produced by successive cambiums either cortical or pericyclic in origin. This type of stem presents a striking resemblance to stems of _Cycas_ and _Macrozamia_ except in the possession of a double cylindrical stele consisting of both centripetal and centrifugal secondary xylem and phloem separated by a zone of primary xylem (partial pith). _Medullosa gigas_ Renault. This species was founded on a piece of stem from the Permian of Autun[268], consisting almost entirely of secondary xylem, which Brongniart had previously placed in his genus _Palaeoxylon_[269]. The secondary xylem reaches a diameter of 45–50 cm. and in the portion of the central region preserved there are a few vascular strands like the star-rings of other species. The considerable development of secondary xylem indicates a form of stem similar to some forms of _M. stellata_ (_e.g._ fig. 416, F), but as the available data are insufficient for accurate determination Renault’s specific name is retained. Renault describes the internal xylem cylinder (_i.e._ the centripetal xylem) as very slightly developed or as hardly visible, a feature in which the French specimen shows a nearer approach to the structure of a recent Cycad. _Medullosa porosa_ Cotta. The second of Cotta’s species[270], which has been fully investigated by Weber and Sterzel, is constructed on the same plan as that of _M. stellata_, but the stem is distinguished by the greater number of star-rings and, more especially, by the presence of an outer system of vascular strands in the axial region (fig. 416, M): these form a frequently interrupted cylinder of anastomosing strands characterised by the feeble development of secondary xylem and phloem or by the absence of this tissue on the outer face of the strands. The component parts of this outer series occasionally fuse with the internal star-rings. _Medullosa Solmsi_ Schenk[271] var. _typica_ Web. and Ster.[272]