The stele is exarch and roughly triangular; except in the broader zone of secondary tissue it agrees with the protostele of _forma α_. The secondary xylem (fig. 439, C) possesses numerous medullary rays 3–4 cells broad and of considerable depth: the secondary phloem is characterised by the presence of thick-walled elements, presumably sieve-tubes, like those of _Medullosa Leuckarti_ and _M. anglica_. The ground-tissue is rich in secretory tissue and the stem-surface, from which the leaf-bases have been detached, is limited by a wide zone of secondary tissue produced by a phellogen. _Sutcliffia Williamsoni_ (Seward). 1876. _Myelopteris_ (_pars_) Williamson, Phil. Trans. R. Soc. Vol. 166, Pl. +ii.+ figs. 7, 8; Pl. +iv.+ fig. 17. 1893. _Rachiopteris Williamsoni_ Seward, Ann. Bot. Vol. +vii.+ p. 1. 1894. _Rachiopteris Williamsoni_ Seward, _ibid._ Vol. +viii.+ p. 207, Pl. +xiii.+ 1906. _Sutcliffia Williamsoni_ Scott, Trans. Linn. Soc. Vol. +vii.+ pt +iv.+ p. 62. In an account of _Myelopteris_ (= _Myeloxylon_) published in 1876 Williamson included some sections of petioles from the Lower Coal Measures which I afterwards with his concurrence transferred to the genus _Rachiopteris_ as _R. Williamsoni_. In _Rachiopteris Williamsoni_ the vascular bundles are concentric and not collateral, and are further distinguished from those of _Myeloxylon_ by the association of parenchyma with the tracheids. In the arrangement of the bundles and in the structure of the ground-tissue the petioles of _Rachiopteris Williamsoni_ agree with those of _Myeloxylon_. An outstanding feature of the vascular strands of the former is the occurrence at fairly regular intervals in the peripheral part of the phloem of comparatively large tubes described by me as secretory canals on the ground that evidence was furnished of their development by the schizogenous separation of cells to form a central canal. The canals were compared with the large sieve-tubes of the Marattiaceae, but with the qualification that ‘their mature form and their manner of development are strongly suggestive of small secretory canals.’ Nothing was known as to the stem which bore these petioles until Scott’s discovery of _Sutcliffia_ with vascular bundles in the cortex and leaf-bases of the same type as those of _Rachiopteris Williamsoni_. As Scott says, there are a few distinguishing features which suggest that _R. Williamsoni_ is not specifically identical with the petioles of _Sutcliffia insignis_, though the agreement is such as to justify the substitution of _Sutcliffia_ for _Rachiopteris_. The tubular elements in the phloem which I considered to be secretory canals are regarded by Scott and Miss de Fraine as sieve-tubes.