The surface of the stem shown in section in fig. 148, A, is composed of broad leaf-cushions. A single leaf-trace with its parichnos passes into each cushion, but in the neighbourhood of the base of a cushion the parichnos bifurcates (cf. fig. 146, H, I) and the arms diverge slightly to the right and left finally passing beyond the cushion into the lamina of the leaf, their position being shown, as already explained, by the two small lateral scars on the leaf-scar area. The diagrammatic sketch of a radial longitudinal section through a leaf-cushion represented in fig. 150 illustrates the relation of the leaf-trace to the leaf-cushion. The trace consists of xylem, _x_, above and a strand of the secretory zone, _st_, below; the parichnos tissue was originally present on the under side of the leaf-trace at _a_. The external surface, _bc_, marks the limit of the leaf-scar through the middle of which passes the vascular strand _lt_. The lower gap _a_ has been formed by the tearing of thin-walled cells of the phellogen, the meristematic tissue from which a considerable amount of secondary cortical tissue or phelloderm has been produced at _pd_. On the outside of the cushion, _c_, the cells are somewhat crushed and distinguished by their darker colour from the bulk of the parenchymatous tissue _d_. This section also illustrates another characteristic feature of _Lepidodendron_, namely the presence of a ligule and a ligular pit: the former is represented by a carbonised patch of tissue and the latter extends from the surface of the cushion at _b_, just above the leaf-scar, almost to the level of the leaf-trace, _lt_. A comparison of this section with figs. 146 and 147 will make clear the relation of the several parts of the cushion and leaf-scar. The gaps _gg_, seen in fig. 148, A and B, mark the position of the delicate meristematic zone or phellogen which arises close to the bases of the leaf-cushions; the phellogen has already produced a few rows of radially disposed elements, represented by short radial lines in the drawing, which constitute secondary cortical tissue. [Illustration: FIG. 150. _Lepidodendron vasculare_. Leaf-cushions in longitudinal section. (From a specimen in Dr Kidston’s Collection.)] In older shoots the amount of the secondary cortical tissue developed on the inner side of the phellogen is considerable (cf. figs. 152, 153). The structure of the cortex of a shoot in which secondary growth, both in the stele and in the outer cortex, has progressed further than in the specimen shown in fig. 148 is represented in fig. 151. [Illustration: FIG. 151. _Lepidodendron vasculare_. An older stem than that shown in fig. 148. (From a section in the Manchester Museum. No. 351.)]