Notes. 
237 
The new genus, the species of which may be said to combine the anatomical 
habit of a Cordaites with the centripetal xylem of a Poroxylon> may be characterized 
as follows:— 
Mesoxylon, gen. nov. 
Pith relatively large, discoid. 1 
Wood dense, with narrow, usually uniseriate medullary rays, and relatively 
small tracheides. 
Leaf-traces double where they leave the pith, the two strands uniting at a lower level, 
but undergoing further subdivision in the pericycle and cortex, before entering the leaf. 
Centripetal xylem present in the stem, where it forms part of the leaf-traces at 
the margin of the pith and throughout their course outwards into the leaves. 
Outer cortex strengthened by a system of sclerenchymatous bands of the 
Dictyoxylon or Sparganum type. 
Throughout the genus the wood is of the kind usual in Cordaitales, the bulk of 
the secondary tracheides having multiseriate bordered pits on the radial walls. 
The tracheides of the leaf-traces, so far as observed, are spiral or scalariform, and 
in some species this is also the case in the inner part of the intermediate secondary wood. 
A brief diagnosis of the species follows :— 
1. Mesoxylon Sulcliffii 2 ; Poroxylon Sutclijfii , Scott, Studies in Fossil Botany, 
2nd edition, 1909, p. 511 ; Fig. 184 (transverse section of stem). 
Leaf-bases crowded, completely covering the surface of the stem. 
Pith large, discoid, with a persistent outer zone. 
Twin-bundles of the leaf-trace, at the margin of the pith, remaining separate 
through several internodes before fusing ; subdividing in the cortex to form about 
eight bundles in all. 
Petiole of leaf flat, containing about sixteen bundles. 
Centripetal xylem distinct, persisting below the point of fusion of the two leaf- 
trace bundles. 
Tracheides of the leaf-traces spiral or scalariform; those of the intermediate 
secondary wood pitted, except sometimes at the extreme inner margin. 
Medullary rays uniseriate, 3-6 cells in height. 
An axillary bud present in the axil of every leaf. 
Dictyoxylon zone of cortex somewhat narrow. 
Roof-nodules; Shore, Littleborough. 
The very numerous sections of this species appear to represent about nine 
distinct specimens. The diameter is pretty uniformly about 3 cm., including the 
leaf-bases, the pith alone having an average diameter of 1*4 cm. This is the only 
species in which anything is known of the leaf. 
2. Mesoxylon poroxyloides , sp. nov. 
Leaf-bases somewhat less crowded than in the preceding species. 
Pith of moderate dimensions, discoid, with a persistent outer zone. 
1 This point is not yet demonstrated in the case of Mesoxylon platypodium ; see below. 
2 The specific name, in honour of the owner of the colliery at Shore (reopened on account of 
its richness in fossil remains), was originally suggested by Mr. J. Lomax, who sent out the sections 
under the name Cordaites Sutcliffii. All the species described are derived from the Shore workings. 
