In comparatively young Stigmarian axes the outer cortex already possesses a band of secondary radially disposed cells characterised by the greater tangential extension of the more external elements; usually this tissue terminates abruptly on the inner edge and the line of separation no doubt marks the position of the phellogen. Occasionally some delicate secondary elements are preserved internal to the phellogen, and these in young specimens form a narrow cylinder composed in part of radially elongated cells showing signs of recent tangential divisions. In its earlier stage of activity the phellogen seems to form a greater amount of secondary tissue on the outside, but this is clearly not of the nature of cork, the tissue which occupies a corresponding position in recent plants. The primary cortex shows no signs of shrinkage or collapse as would be the case were it cut off from the vascular system by a zone of impermeable cork. Fig. 210, G, represents a piece of the external tissue of a specimen in which the slightly flattened xylem cylinder measures 1·4 × 1 cm.; the inner cortex has disappeared and fragments only of the middle cortex are preserved. The outer cortex, with an average breadth of 2 mm., consists superficially of primary parenchyma with a somewhat uneven surface and with a rootlet attached here and there; a short distance below the surface is a band of conspicuous cells, _b_, characterised by dark contents suggesting very imperfectly preserved fungal hyphae, but the nature of the substance filling the cells cannot be made out with certainty. It is, however, interesting to find that this dark band constitutes an obvious feature (fig. 210 H, _b_); its position is comparable with that of the dark-walled cells in the outer cortex of rootlets. A short distance internal to this dark band tangentially elongated cells form the outermost elements of the secondary cortex; these become gradually narrower towards the interior and pass into radial series of smaller cells of uniform size, as seen on the inner edge of fig. 210, G. At the inner boundary of this tissue, just below the region shown at the bottom of the drawing, was situated the phellogen. Such traces of tissue as occur on the inner side of the line where splitting has usually occurred, consist of thinner elements with recently formed tangential walls and probably represent an early stage in the development of phelloderm.