Some species of _Medullosa_ probably resembled in habit _Angiopteris evecta_ and the larger Marattias; they had short and relatively thick stems clothed with the large decurrent bases of long compound fronds superficially like those of some recent Ferns and the leaves of the Cycad _Bowenia_. It is probable that, as Zeiller[238] has pointed out, the fronds of _Medullosa_ and of other Pteridosperms had a greater tendency than those of true Ferns to a dichotomy of the rachis. In other types the stems reached a considerable length and leaves and branches were separated by several feet of bare stem. The large size of the leaf-stalks in proportion to the diameter of the stem as shown by such species as _Medullosa anglica_ and _M. Leuckarti_ (fig. 416) suggests either a short and thick main axis or, in the case of long stems bearing scattered leaves, a plant that supported itself partially at least by a habit of growth comparable with that of tropical Aroids or other lianes. While _Medullosa anglica_ with its contiguous leaf-bases affords an example of the first type, the occurrence of stems of a Permian species, _M. stellata_, 3½ metres long without branches or leaf-scars, suggests the habit of a liane; similarly a specimen of _Medullosa Leuckarti_ in the Chemnitz Museum bearing a few spreading petioles but little narrower than the stem and given off at a wide angle would seem to favour the view that some species were ill adapted to be mechanically self-supporting plants. The longest piece of stem that has come under my notice is a specimen of _M. stellata_ in the Chemnitz Museum reaching a length of nearly 8 metres: some species attained a diameter of about 50 centimetres. _Medullosa_ is always polystelic: the plan of the vascular system varies considerably as regards both the number and form of the steles, but there is a uniform type of structure within the limits of each stele that recalls the single stele of _Heterangium_. The steles consist of a central region composed of primary xylem, originally surrounded by phloem, which in its mesarch or exarch structure agrees with the vascular tissue of some species of _Gleichenia_ or _Lygodium_. To this central region a cambium added secondary xylem and phloem either in the form of a cylinder of uniform breadth, or more frequently the centrifugally developed xylem exceeded in amount the secondary conducting tissue added to the inner side of the primary region. Apart from anatomical details a Medullosan stem with its several steles, each with secondary tissue, embedded in parenchymatous ground-tissue resembles the stems of some Dicotyledonous climbers such as _Thinouia scandens_, species of _Serjania_ and _Paullinia_[239].