Scott[216] has recently published a note in which he states that most of the British Coal Measures Heterangiums were polydesmic. Two bundles, and not a single strand as in the Scotch _H. Grievii_, leave the stele for each leaf, and these divide into four, in some cases at least, before entering the petiole. The secondary xylem is continuous at its inner edge with the outermost primary tracheids (fig. 411, A′) and consists of rows of tracheids, 1–3 elements broad, alternating with numerous broad medullary rays of radially elongated parenchyma. Beyond a typical cambium-zone the secondary phloem consists of parenchyma and sieve-tubes bounded by crushed arcs of primary phloem. Abutting on the phloem is a pericycle composed of several layers of small parenchymatous cells (fig. 411, A, _p_) and in the outer layers of this tissue a phellogen (fig. 411, C, _p_) and some periderm are usually present though, as Williamson and Scott point out, the periderm is less regular and narrower than in _Lyginopteris_. The inner cortex, composed of short parenchymatous cells, is traversed by numerous narrow bands of dark, thick-walled cells similar in the structure of the elements, though peculiar in the horizontal elongation of the groups, to the sclerous nests in the pericycle and pith of _Lyginopteris_. These characteristic bands are chiefly seen in the oblique longitudinal section of a stem represented in fig. 412. In this section, 25 mm. in length, the lighter band, _p_, is the pericycle and in it a few obliquely cut leaf-traces are shown as dark patches. The horizontal bands are similar in structure and shape to the diaphragms of thick cells in the pith of _Abies magnifica_[217], and in both plants they probably serve as supports to the softer parenchyma. There may be as many as 46 bands in a vertical length of cortex of 1 inch (about 19 per centimetre). It was the occurrence of precisely similar transverse lines on the carbonised impressions of the rachis of _Sphenopteris elegans_ that led Kidston[218] to suggest a connexion between that species and the stem of _Heterangium Grievii_. The outer cortex, consisting of alternate strands of parenchyma and stereome similar to that of _Lyginopteris_, is much narrower and a less conspicuous feature than in _Heterangium_; the stereome bands do not form so regular a hypodermal network and extend much further vertically without anastomosing. The epidermis has been described as a layer of fairly thick cells showing in one case an appearance of a depressed stoma[219]. There are no secretory canals like those of Cycads but, as in _Lyginopteris_, scattered cells with dark contents in the stem-tissues probably represent secretory sacs. The leaf-traces on leaving the stele pursue a very gradually ascending course to the petiole; they retain their collateral structure in the pericycle and cortex and have no secondary xylem, but become concentric as they enter the base of a leaf.