The inner edge of the phelloderm seen at _e_ in fig. 151, C, passes suddenly into the inner primary region of the outer cortex (fig. 151, A and C, _g_) which comprises two types of parenchymatous tissue, patches of isodiametric cells, _g_, _g_, alternating with radially arranged areas consisting of tangentially elongated elements (fig. C, _f_, _f_; fig. D) which extend as wedges into the phelloderm. The longitudinal section represented in fig. 152, B, shows an equal bifurcation of a stem in which no secondary xylem is present; in the lower part of the section the xylem and the outgoing leaf-traces are seen in radial section and at the upper end of each arm the leaf-traces alone, _lt_, are exposed, as in fig. 148, B. It is interesting to notice the large amount of phelloderm which has been produced in the fork of the branch, at _pd_, where greater strength is required. [Illustration: FIG. 152. _Lepidodendron vasculare._ Sections of dichotomously branched shoot. A. From a section (10·5 × 9 cm.) in the Cambridge Botany School Collection. B. From a section (8 cm. long) in the Cambridge Collection.] The section represented diagrammatically in fig. 152, A, has lost the outermost part of the cortex together with the leaf-cushions; it consists largely of secondary cortex composed of radially disposed phelloderm cells and tangentially placed secretory strands (represented by the discontinuous black lines in the drawing): the dotted region in the central part of the axis is composed of primary cortical parenchyma, and the two spaces surrounding the steles contain portions of the lacunar middle cortex. Each stele possesses a narrow crescentic zone of secondary xylem; the amount is greater in the case of the right-hand stele, of which a small piece is shown on a larger scale; the striking contrast in size between the outer and more internal secondary tracheae is no doubt the expression of some unfavourable condition of growth. The position of the secretory zone beyond the secondary xylem is shown at _sc_, fig. 152, A. [Illustration: FIG. 153. _Lepidodendron vasculare._ (From a specimen (16 × 7·5 cm.) in the Manchester Museum.)] An example of a large and partially decorticated stem is afforded by the specimen (16 × 7·5 cm.) shown in fig. 153. The irregularly ribbed surface is formed of rather thick-walled phelloderm, in which occur tangentially arranged rows of secretory strands. The tapered form of the secondary cortex as it abuts internally on the primary cortex is shown very clearly in the drawing (cf. fig. 151, C). The stele in this much older stem consists mainly of secondary wood. [Illustration: FIG. 154. _Lepidodendron vasculare._ Shoot (2·8 cm. diam.) with two steles. (From a specimen from Halifax in the Williamson Collection, British Museum, No. 340.)]