and short reticulately pitted cells. Each leaf-trace can be followed through approximately four internodes before its individuality is lost in the general mass of metaxylem. The disposition of the peripheral traces is such as to justify the conclusion that the phyllotaxis of the stem is ⅖.[467] [Illustration: Fig. 446. _Megaloxylon Scotti._ A, B. Transverse and longitudinal sections. _x¹_, _x²_, primary and secondary xylem; _lt_, leaf-traces. Nat. size. C. Secondary xylem.] [Illustration: Fig. 447. _Megaloxylon Scotti._ Transverse section of the primary portion of the stele with leaf-traces, _lt_, and the inner edge of the secondary xylem.] [Illustration: Fig. 448. _Megaloxylon Scotti._ A, transverse section at the junction of the primary and secondary tissues; B, longitudinal section showing the inner edge of the secondary xylem, _x²_, a leaf-trace, _lt_, and the metaxylem, _m_.] The secondary xylem (fig. 446, C) resembles that of _Lyginopteris_ and _Heterangium_ though it is less parenchymatous. The medullary rays are numerous and vary in breadth from 1 to 5 cells, while the tracheids, with multiseriate bordered pits on their radial walls, form bands 1 to 8 elements in breadth. There are no regular rings of growth but occasional arcs of narrow tracheids interfere slightly with the otherwise uniform structure of the wood. A leaf-trace in its oblique outward course through the wood becomes completely enclosed by a cylinder of secondary xylem and thus appears to be concentric. Owing to the absence of any tissue external to the secondary xylem of the stem, statements as to the subsequent behaviour of the leaf-traces on emerging from the stele are purely hypothetical. It is, however, not improbable that each concentric trace lost its secondary tissue and broke up into several collateral strands, a suggestion based on the behaviour of the leaf-traces in _Medullosa anglica_.