Leaf-traces are furnished by the primary xylem at the edge of the ‘partial pith’ of the outer stele: as a leaf-trace passes outwards through the outer cylinder of secondary xylem the cambium invests it with secondary xylem and phloem, but as it passes through the cortex of the stem it becomes reduced to its primary elements, and by successive branching gives rise to small collateral bundles which enter the petioles. The piece of stem shown in fig. 416, G, illustrates the exit of leaf-traces from the stele and their subsequent division into several small bundles, _v_, which are scattered in the cortex with strands of sclerenchyma. In a specimen identified with _Medullosa stellata_, Schenk[261] found part of a leaf-base attached to the stem: its vascular system was of the _Myeloxylon_ type, the bundles being identical with those in the cortex of the stem seen in fig. 416, G. In some stems of _M. stellata_ the outer, centrifugally developed, portion of the main stele is very much broader than in the example represented in fig. 416, D. The diagrammatic sketch reproduced in fig. 416, F, represents a section of a Chemnitz specimen in the British Museum[262] in which the axial region containing several star-rings is almost enclosed by an inner zone of secondary xylem, and beyond the narrow primary xylem (black in the sketch) the rest of the block consists exclusively of secondary xylem 5·5 cm. broad. This example illustrates a common tendency in _Medullosa_ towards a large excess of centrifugal over centripetal secondary vascular tissue. A similar specimen of _Medullosa stellata_ is figured by Mougeot[263] from the Vosges showing a considerable development of centrifugal xylem comparable with that in the British Museum stem. Weber and Sterzel[264] describe stems of _Medullosa stellata_ showing slight periodic swellings which it is suggested, though there is no evidence in support of the opinion, may be connected with reproductive organs. * * * * * _Medullosa stellata_ var. _corticata_[265]. The specimen referred to this variety, represented in fig. 416, G, has already been quoted as affording data with regard to the origin and behaviour of the leaf-traces. In this type of stem the outer portion of the main stele is narrower than in _M. stellata_ var. _typica_ and the stele never forms a complete tube. The star-rings in the centre of the stem are more numerous than in the type-species of the genus. In the axial region of some stems included in the form-cycle to which _M. stellata_ belongs there may be flatter and tangentially elongated vascular strands in addition to the cylindrical star-rings; these are termed plate-rings. * * * * *