The first account of the anatomy of _Sigillaria_ we owe to Brongniart[517] who published a description of the internal structure of an agatised stem, about 4 cm. in diameter, from Autun, which he referred to _Sigillaria elegans_. It has, however, been shown by Zeiller[518] and by Renault that this petrified fragment belongs to Brongniart’s species _S. Menardi_, which is probably a young form of _S. Brardi_. Brongniart’s specimen, now preserved in the Paris Natural History Museum, is a very beautiful example of a silicified plant: on part of the surface are preserved the hexagonal contiguous leaf-scars, like those shown in fig. 193, A, and on the polished transverse section is seen a relatively large stele consisting of a ring of secondary xylem surrounding a series of crescentic groups of primary xylem (fig. 200, A) enclosing a wide pith occupied by concentric layers of silica. A portion of the outer cortex is preserved, and this is separated from the stele by a broad space filled with siliceous rock. The main features of this type may be described in a few words. The primary xylem differs from that of such Lepidodendron stems as have been described in being made up of groups of scalariform and occasionally reticulate (fig. 200, C) tracheae, having a plano-convex or more or less crescentic form as seen in transverse section. These primary strands, in contact with one another laterally, have their narrowest elements on the outer edge. The leaf-traces are given off from the middle of the abaxial face of each xylem strand (fig. 202, C, _lt_); these pass obliquely outwards through medullary rays and then, as in _Lepidodendron_, turn sharply upwards before bending outwards again on their way to the leaves. Each leaf-trace consists of a group of primary tracheae to which a few secondary tracheae are added during the passage through the secondary wood. The secondary xylem forms a continuous cylinder of tracheae with scalariform bands on both radial and tangential walls; the medullary rays are numerous and consist of long and narrow series, usually one cell broad, of parenchymatous cells with occasional short rays one or more cells in depth. The slightly greater breadth of the rays between each primary xylem strand tends to divide the secondary wood into bundles corresponding in breadth to the primary groups. The outer cortex closely resembles that of _Lepidodendron_; it consists internally of radial series of secondary, elongated and rather stout, elements abutting on the parenchymatous tissue of the leaf-cushions.