occasionally preserved in wonderful perfection[122]. No endodermis has been recognised. Sclerous nests are scattered in the ground-tissue as are also secretory sacs (figs. 404, E; 405, A). A small root _r_ has penetrated the parenchyma of the rachis shown in fig. 405, A. [Illustration: Fig. 405. _Lyginopteris oldhamia_. A, petiole section; _a_, glandular emergence; _r_, root. B, stalked gland; _s_, stoma. C, inner edge of wood of a stem; _c_, arc of inversely orientated vascular tissue. D, D’, part of a frond of _Sphenopteris Hoeninghausi_. E, part of axis of D. (A, C, D, Kidston Coll.; B, Manchester Coll. R. 645.)] [Illustration: Fig. 406. _Lyginopteris oldhamia._ Transverse section illustrating branching of petiole. × 5. (From a drawing supplied by Prof. Oliver.)] _Sphenopteris Hoeninghausi_ Brongn.[123], founded on material from English Coal Measures, was regarded by Williamson as the foliage of _Lyginopteris_ chiefly on the ground of the occurrence of emergences on the axes (figs. 404, A, B) and laminae of the impressions like those on the petrified stems, and this comparison received support from the resemblance of the fragments of pinnules associated with _Lyginopteris_ and its petioles in the calcareous nodules to the leaflets of Brongniart’s type. This identification is supported by subsequent work. The quadripinnate fronds, which attain a considerable size, resemble those of recent species of _Davallia_ and other ferns, but the forking of the rachis and branches of the frond is a striking feature: the pinnae may reach a length of 15 cm.[124] The portion of carbonised rachis shown in fig. 405, E, reveals the existence of a hypodermal reticulum like that in the outer cortex of a _Lyginopteris_ stem and the same feature is seen in the more slender axis represented in fig. 404, A, at _b_.[125] The pinnules are usually deeply lobed and the segments may be comparatively broad and blunt or narrow[126] (fig. 290, C, vol. +ii.+ p. 399; fig. 404, A, _a_, B; fig. 405, D’). The lamina has a well marked dorsiventral structure: the palisade-tissue next the upper surface is separated from the epidermis by small hypodermal cells, possibly functioning as a water-storage layer, and the central part of the mesophyll consists of loose aerenchyma: the veins are collateral as in recent ferns and stomata occur in the lower epidermis. Emergences are seen both on impressions (fig. 405, D’) and on petrified specimens. A striking feature of the pinnules is the rounded surface caused by the revolute edge of the lamina as seen in the section reproduced in fig. 404, B. This character coupled with the occasional occurrence of groups of short tracheal elements at the termination of the veins denotes a tendency to a xerophilous habit.