A protoxylem of a meristele still attached to the central protostele occupies an internal position, and at a higher level, as separation of the meristele is effected, the spiral tracheids occur on the inner face. New meristeles are given off at intervals from the main stele ‘to compensate for those parts of the reticulum which were used up in the formation of leaf-trace strands[411].’ The meristeles form the starting-point for the leaf-traces, an intermediate system between the main stele and the actual leaf-traces; they differ, therefore, from the parent leaf-traces of _Medullosa anglica_, which are completely used up by repeated subdivision. Moreover in _Sutcliffia_ the leaf-bundles are concentric and not collateral. [Illustration: Fig. 439. _Sutcliffia insignia_ Scott. A, B, E, forma α. (After Scott.) C, D, forma β. (After de Fraine.) A. Transverse section of stem; _a_, _b_, double rows of leaf-trace bundles. The larger black masses are the meristeles; the smaller patches represent bundles derived from the meristeles. B. Longitudinal section of a radially symmetrical bundle from a leaf-base. C. The junction between the primary and secondary xylem. D. Vascular system in transverse section: _m_, _m′_, meristeles; _s_, main stele; _e_, extrafascicular strands; _lt_, leaf-traces; _c_, secondary cortex. E. Vascular bundle from petiole showing a ring of large sieve-tubes surrounding the xylem, and portions of stereome strands.] [Illustration: Fig. 440. _Sutcliffia insignis._ Part of the primary xylem showing on the upper edge the beginning of secondary growth. (Cambridge Botany School, 560.)]