The single meristele subsequently divides into two equal portions preparatory to the bifurcation of the petiole (fig. 406). The inner cortex, consisting of parenchymatous tissue and many secretory cells with an occasional group of sclerenchymatous elements in place of the abundant nests of this tissue in the pericycle, has been invaded in the stem shown in fig. 403 by numerous rootlets of _Stigmaria_ and _Lyginopteris_, some of which are seen interrupting the continuity of the outer cortex. The greater width of the cortical region at _f_, fig. 403, is due to the decurrent base of a petiole the meristele of which is not included in the section. The lighter and broader bands between the cross-sections of the stereome-network in the outer cortex are occupied by remains of tangentially stretched parenchymatous cells, and beyond this zone in a younger stem there are a few layers of parenchyma forming the superficial tissue, but there appears to be no well-defined epidermal layer. [Illustration: Fig. 404. _Lyginopteris oldhamia._ A, B. Frond fragments; _a_, pinnule; _b_, reticulum of sclerenchyma. C. Portion of stele of the stem reproduced in fig. 402. D. _px_, protoxylem; _s_, sclerenchyma; leaf-trace close to the edge of the secondary xylem; _p_, periderm. E. Petiole; _m_, meristele. (A, Kidston Coll. 664 B; B, Camb. Botany School 508; C, Binney Coll. 179; D, E, Camb. Botany School, 93, 159.)] Young stems have been recognised in which there is very little secondary xylem and phloem: in these the stereome bands in the outer cortex are closer together than in the stretched hypodermal tissue of older shoots and the scattered sclerous nests are represented by unthickened cells. In addition to young stems Williamson and Scott described a distinct type of small stem in which the primary xylem forms an almost complete ring[107] comparable with the primary xylem of some adult Sigillarian stems (vol. +ii.+ p. 220) but distinguished by its mesarch structure and by the reticulate pitting of the centripetal xylem. A characteristic feature of the stem is the occurrence of emergences from the outer cortex which have the structure either of spinous processes, broadly linear or flask-shaped, or of stalked glands[108]. A portion of a glandular emergence is shown in fig. 405, B: the group of small cells immediately below the blunt apex is in this instance still intact though showing signs of disorganisation in the centre; but in many cases the secretory tissue has not been preserved and the head of the emergence is occupied by a space. A single stoma is seen at _s_ in longitudinal section. Further reference to the emergences is made in the description of the leaf.