Mas ten — The Structure of Mesoxylon Stttcliffii (Scott). 385 
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. 
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 inter- 
mediate secondary wood. 
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. 
Outer cortex strengthened by a system of sclerenchymatous bands of the 
Dictyoxylon or Sparganum type. 
Mesoxylon Sutcliffii. 
(Poroxylon Sutcliffii, Scott, Studies in Fossil Botany, 2nd ed., 1909, 
p. 5 11 . Fig- i8 4 )- 
II. General Characters. 
The general characters of the genus Mesoxylon have already been 
described (p. 384) ; it is proposed now to give those of our most fully 
known species, Mesoxylon Sutcliffii. The specific name, in honour of the 
owner of the colliery at Shore (reopened on account of its richness in fossil 
remains, and whence all the species have been obtained), was originally 
suggested by Mr. J. Lomax, who sent out the sections under the name 
Cordaites Sutcliffii. 
At present only the stem, the leaf-bases, and the lower part of the 
petiole are known, and this is the only species of Mesoxylon in which any- 
thing is known of any part of the leaf other than the adherent leaf-bases. 
The stem of Mesoxylon Sutcliffii as represented by the numerous series of 
sections which have been examined in the preparation of this paper — 
belonging to at least nine distinct specimens — shows remarkably little 
variation in size. All the specimens have been somewhat flattened by 
pressure, but the average diameter, including the leaf-bases, is about 3 cm., 
with a variation of only about 0*2 cm. around this size. The stem is some- 
what larger than that of any of the other species of Mesoxylon described in 
our preliminary note, excepting M. Lomaxii, which is of considerably larger 
size, being about 5 cm. in diameter. Several of these species were, however, 
described from single specimens, and the discovery of others will doubtless 
show that all the species vary considerably in size. 
Comparing Mesoxylon Sutcliffii with the French forms of Poroxylon, 
