Maslen.— The Structure of Mesoxylon Sutcliffii (Scott). 409 
resting buds of some kind, but whether vegetative or reproductive it has 
been impossible to determine. In the only other species of Mesoxylon in 
which axillary members are present, viz. M. multirame , a leafless axillary 
branch, resembling a phylloclade, is present in most of the leaf axils 1 ; 
these are very different from the little buds of M. Sutcliffii , and evidently 
the two organs had quite distinct functions. 
An epitome of the generic characters of Mesoxylon has already been 
given (see pp. 384, 385), and the following is a brief diagnosis of the species 
described in the present paper. A full account of the other species of Meso- 
xylon will be given in a forthcoming paper by Dr. D. H. Scott, F.R.S. 
VIII. Mesoxylon Sutcliffii (Poroxylon Sutcliffii , Scott, Studies in Fossil 
Botany, 2nd Edition, 1909, p. 51 1, Fig. 184). 
Only the stem and bases of leaves known. 
Leaf-bases crowded, completely covering the surface of the stem. 
Pith large (diameter nearly half that of the stem as a whole), discoid, with 
a persistent outer zone. 
Twin-bundles of the leaf-traces, when they reach the margin of the pith, 
separated by tissue about equal in width to that of one of the bundles, 
and remaining separate when traced downwards through several inter- 
nodes before fusing ; subdividing in the pericycle and cortex to form 
about eight bundles in all. 
Centripetal xylem distinct, persisting below the point of fusion of the two 
leaf-trace bundles. 
Traeheides of the leaf-traces (centripetal and centrifugal), spiral or scalari- 
form ; those of the intermediate secondary wood pitted, except perhaps 
at the extreme inner margin. 
Medullary rays of the secondary xylem uniseriate, usually 1-6 cells in 
height. 
Dictyoxylon zone of cortex somewhat narrow. 
Petiole of leaf flattened, containing about sixteen bundles near its insertion 
on the stem. 
An axillary bud present in the axil of every leaf. 
Roof nodules ; Shore, Littleborough. 
IX. Conclusions. 
Mesoxylon Sutcliffii (as well as the other species of Mesoxylon ) exhibits 
structural characters intermediate between those of Cordaites and Poroxylon , 
but on the whole stands much nearer to the former genus ; indeed, it seems 
not improbable that many of the familiar Cordaitean leaves which occur in 
the English Coal Measures may really belong to the new genus. 
1 Scott and Maslen, Preliminary Note, p. 238. 
