[Illustration: FIG. 162. _Lepidodendron fuliginosum._ Part of the stele in transverse section. (Binney Collection, Sedgwick Museum, Cambridge.)] [Illustration: FIG. 163. _Lepidodendron fuliginosum._ Longitudinal section. (Binney Collection, Cambridge.)] Figs. 162 and 163 illustrate the structure of the outer portion of the xylem and adjacent tissues in a section of a shoot 3·8 cm. × 2·5 cm. in diameter, which is in the act of branching, as shown by the occurrence of two steles of equal size. A figure of the complete section will be found in Binney’s memoir[324], and additional illustrations were published in 1899[325]. [Illustration: FIG. 164. _Lepidodendron fuliginosum_. Leaf-trace. (Binney Collection, Cambridge.)] The primary xylem (figs. 162, 163, _x_) is succeeded by 2–3 rows of polygonal cells with dark contents and associated with isodiametric tracheae: these pass into clearer parenchymatous tissue, _a_, characterised by the arrangement of the cells in vertical series, to which the term meristematic zone has been applied. The secretory zone, _s_, abutting on the meristematic zone, consists of more or less disorganised parenchymatous cells and broader and more elongated spaces; it is interrupted here and there by an outgoing leaf-trace, as at _lt_ 1 and _lt_ 2 in fig. 162. The secretory zone is succeeded by a homogeneous inner cortex like that described in _L. vasculare_; part of this region is seen at the upper edge of fig. 162. The broad middle cortex, which is separated from the inner cortex by a sharply defined boundary, is composed of rather small lacunar parenchymatous tissue consisting of sinuous tubular elements interspersed among isodiametric cells of various sizes (fig. 166, _p_). In the middle cortical region the leaf-traces pursue an almost horizontal course; one is shown in fig. 164, in oblique longitudinal section, in a reversed position; the xylem, _x_, should be on the inner side of the secretory tissue, _s_. The clear space between the two parts of the vascular bundle was originally occupied by a few layers of parenchymatous cells, as seen in the transverse sections, figs. 165 and 166. In some specimens the leaf-traces pass through the middle cortex in a much more vertical course, as shown by the section represented in fig. 165. This section illustrates the structure of a typical leaf-trace with unusual clearness; it shows the tangentially elongated group of xylem, the strand of tissue which occupies the position of phloem, _s_ (to which the term secretory zone is applied), the compact parenchyma between the two parts of the bundle, and surrounding the whole a narrow sheath sharply contrasted by the smaller and more uniform size of the cells from the middle cortex, a few cells of which are seen in the photograph. The middle cortex shows a well-defined junction with the more compact outer cortical region, which consists of primary parenchyma passing externally into a zone of phelloderm composed of