1899. _Lyginopteris oldhamia_, Potonié, Lehrbuch der Pflanzenpalaeontologie, p. 171. ii. _Leaf_. 1828. _Sphenopteris Hoeninghausi_, Brongniart, Prodrome, p. 51. 1872. _Edraxylon_, Williamson, Proc. R. Soc. vol. +xx.+ p. 438. 1874. _Rachiopteris aspera_, Williamson, Phil. Trans. R. Soc. vol. +clxiv.+ p. 684. 1877. _Calymmatotheca Hoeninghausi_, Stur, Culm Flora, +ii.+ p. 266. 1905. _Crossotheca Hoeninghausi_, Kidston, Proc. R. Soc. vol. +lxxvi.+ p. 358. iii. _Seed_. 1877. _Lagenostoma_, Williamson, Phil. Trans. R. Soc. vol. +clxvii.+ p. 234. 1903. _Lagenostoma Lomaxi_, Oliver and Scott, Proc. R. Soc. vol. +lxxi.+ p. 477. iv. _Root_. 1876. _Kaloxylon Hookeri_, Williamson, Phil. Trans. R. Soc. vol. +clxvi.+ p. 23. [Illustration: Fig. 402. _Lyginopteris oldhamia_. Transverse section of the type-specimen in the Binney Collection, Sedgwick Museum, Cambridge. (After Arber.)] i. _Stem_. The petrified stem on which Binney founded the species was first figured by Dr Arber[105] from a section in the Binney collection in the Sedgwick Museum, Cambridge: this section (13 mm. in diameter) is reproduced in fig. 402. The most striking features are: (i) the pith consisting of an unusually large and irregular group of dark thick-walled parenchyma, (ii) the broad cylinder of manoxylic secondary xylem characterised by multiseriate medullary rays, (iii) the outer cortex composed of dark radially disposed and oblique bands of mechanical tissue separated from one another by partially destroyed and tangentially elongated parenchymatous elements. It is this outer cortex that Williamson aptly compared with the Roman numerals on a clock-face. In the perimedullary region and in contact with the inner edge of the secondary-xylem cylinder are six strands of primary xylem representing the xylem halves of collateral bundles separated from the primary phloem strands by the intervening cylinder of secondary wood. Two of the primary xylem strands in lateral contact are seen in fig. 404, C; the other four occur as separate bundles. Each primary xylem strand contains a small group of spirally thickened protoxylem elements (_px_) associated with a few parenchymatous cells. The large primary tracheids internal to the protoxylem are characterised by multiseriate bordered pits on their walls, while those external to the protoxylem, which are in contact with the innermost secondary tracheids, have scalariform pitting. The dark patch _s_ (fig. 404, C) is a portion of the large group of sclerenchymatous cells, shown in figs. 402, 403. The perimedullary xylem strands of mesarch structure are the lower portions of leaf-traces and, as Scott points out, ‘each of the bundles surrounding the pith is, in fact, a sympodium, composed of the united lower ends of successive adjacent leaf-traces.’ The larger of the two bundles shown in fig. 404, C, is on the point of passing out to a leaf,