500 FILICALES 
xylem band, flattened on its inner and outer faces. These strands branch 
off from the central stele with the minimum of disturbance, after the 
manner of the strobiloid Pteridophytes. A similarly simple origin of the 
leaf-trace has been seen also in species of Botryopter’s, in which the stele 
is as little differentiated as in Gvammatopterts: there is indeed an entire 
absence of well-marked protoxylem in the stele of Sotryopter’s. In 
Zygopteris also the origin of the leaf-trace is essentially the same, though 
here the matter is complicated by the curious differentiation of the 
xylem of the stele: there is an outer band consisting of larger, scalariform 
Fic. 270. 
Zygopleris Grayi. Transverse section of stele, showing wood and remains of phloem. 
1-5 the five angles of the wood, from which leaf-traces are given off, in order of the 
phyllotaxis, No. 5 belonging to the lowest of the series. 2, principal ring of xylem ; 
é, small tracheides of internal xylem ; -ve, small tracheides at periphery ; 47, phloem; 
r, base of adventitious root. x14. Will. Coll. »1919, B. (From Scott’ 5 Studies tn Fossil 
Botany.) 
tracheides, and a central core consisting of parenchyma together with a 
system of smaller tracheides: both of these contribute to the strand of 
the leaf-trace, which is abstricted off from the ray-like projections of the 
cauline stele (Fig. 270). A new genus from the lower Coal Measures 
has recently been described by Scott,! which is characterised by radially 
seriated wood, apparently of a secondary character: in other respects it 
had much in common with Zygopéer’s. This is the first evidence of 
secondary thickening in the Botryopterideae: the fossil has been named 
Botrychioxylon: but as the sporophylls have not yet been described, 
this very allusive name must be understood only to convey the fact that 
it is a Botryopterid showing secondary growth, just as Bo¢rychiwm is an 
‘Journ. R. Micr, Soc., 1906, p. 519. 
