459, A, show the primary xylem, and the protoxylem is seen in fig. 459, C. A stem described by Dawson[515] as _Asteropteris noveboracensis_ from Devonian beds is compared by him with Unger’s _Cladoxylon mirabile_ and regarded as possibly allied to it. The radial plates of xylem in Dawson’s plant meet in the centre like those of _Asterochlaena_ and the leaf-traces are of the Clepsydropsoid type. [Illustration: Fig. 459. A, _Cladoxylon mirabile_, section of stem; B, _Cladoxylon taeniatum_, section of stem; C, _Cladoxylon dubium_, section of stele; D, _C. dubium_, section of stem; E, _Cladoxylon (?) mirabile_, section of petiole; F, _Syncardia pusilla_; G, development of leaf-trace in _Cladoxylon taeniatum_. (A–E, after Solms-Laubach; F, after Unger; G. after P. Bertrand.)] The type of stem for which Unger founded his genus _Schizoxylon_ is represented in fig. 459, B; there are five small steles in the centre and external to these eleven radially arranged plates, with oval steles between them, in the peripheral region of the stem. Each stele consists of primary (black in the figure) and secondary xylem and agrees with the steles in the other stems. From the type of stem illustrated by _Cladoxylon mirabile_ to that on which the genera _Arctopodium_[516] and _Hierogramma_[517] were founded is a very small step: the vascular tissue has the same characters both as regards gross and minute anatomy, but there is no evidence of cambial activity in the stems referred to the two latter genera, a difference in itself hardly worthy of generic recognition.