. Fossil plants : for students of botany and geology . Paleobotany. XXXII] STENOMYELON 183 from Sutcliffia. The sclerenchymatous bands in the inner cortex of Heterangium are unrepresented in Rhetinangium, and in the latter genus the abundance of secretory sacs and ducts is a characteristic feature, moreover in Rhetinangium, the leaf-trace consists of several groups of primary xylem-elements. Dr Gordon regards Megaloxylon as the type which comes nearest to Rhetin- angium; but the differences in the structure of the secondary wood and the marked contrast between the leaf-traces are too pronounce
. Fossil plants : for students of botany and geology . Paleobotany. XXXII] STENOMYELON 183 from Sutcliffia. The sclerenchymatous bands in the inner cortex of Heterangium are unrepresented in Rhetinangium, and in the latter genus the abundance of secretory sacs and ducts is a characteristic feature, moreover in Rhetinangium, the leaf-trace consists of several groups of primary xylem-elements. Dr Gordon regards Megaloxylon as the type which comes nearest to Rhetin- angium; but the differences in the structure of the secondary wood and the marked contrast between the leaf-traces are too pronounced to justify a preference for Megaloxylon over Heter- angium in the order of affinity. Gordon considers that the undivided leaf-trace of Rhetinangium may represent a forni transitional between the simple leaf-trace of Lygincpteris and the much divided type in Medullosa. The external position of the protoxylem is a character to which too much weight may easily be attached: the difference in position between the protoxylem of Rhetinangium and Heterangium is in some examples of the latter genus hardly perceptible. Kubart^ speaks of the stele of his species Heterangium Sturi as being almost exarch. The incon- stancy in the position of the protoxylem in the xylem of Osmun- daceous stems and in the primary bundles of Eristophyton and other Palaeozoic genera is worthy of consideration in this connexion. STENOMYELEAE. Stenomyelon. Kidston. Stenomyelon tuedianum Kidston. The specimens on which this monotypic genus is founded^ were obtained from the Lower. Fig. 451. Stenomyelon tuedianum Kidst. Transverse section of stem. The black patches represent leaf-traces. (After Kidston; x 14.) Carboniferous rocks (Calciferous Sandstone series) at Norham Bridge, Berwickshire, Scotland. They consist of petrified pieces of a flattened stem, a fragment of a rachis and portions of laminae: 1 Kubart (14). ' Kidston and Gwynne-Vaughan (12).. Please note that these images are extracted from scanned page
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