936 PROFESSOR W. C. WILLIAMSON AND DR. D. H. SCOTT ON THE 
reasonably assume that in this case there were six distinct groups of protexylem, as 
in some of the species of Sphenophyllum investigated by M. Renautt (see Plate 76, 
photograph 24, from the Autun form). It is noticeable that the whole periphery of 
the woody mass is occupied by elements decidedly smaller than those of the interior. 
There is not the slightest indication of a pith, or of any parenchymatous cells among 
the thick-walled trachexw. Longitudinal sections show trachez only, the larger of 
which appear to have pitted walls. One section (see Plate 85, fig. 54) which 
probably passed through the xylem near one of its angles, also shows scalariform and 
spiral trachez ; the latter are small and no doubt represent the protoxylem. 
The soft tissues surrounding the wood have entirely perished, except for a mere 
structureless film, which, in one specimen, extends between the angles of the wood. 
In one of the smaller specimens (see Plate 86, photograph 26) the xylem-strand is 
excessively slender, and its angles acute, though here also there are some indications 
of a double group of protoxylem at each. It is doubtful whether these small 
specimens are identical with the larger ones, which have a massive strand of xylem. 
It is possible that they may belong to a second species, but we have not sufficient 
evidence to justify their separation. The spores of the larger and smaller strobili 
show no constant difference in size. 
The specimen from which fig. 54 is drawn, evidently belongs to the smaller form; 
the diameter of the whole strobilus is only about 6 millims., while those of the larger 
type are on the average at least 12 millims. in diameter. 
The outer cortex of the axis is well preserved. Its inner cells are thin-walled and 
parenchymatous, but towards the exterior they have thicker walls and are more 
prosenchymatous in form. 
As regards the course of the leaf-trace bundles running out into the bracts, our 
data are incomplete. None of our sections show the out-going bundles at the point 
where they diverge. from the central cylinder. On the other hand we have some 
excellent preparations showing the bundles in the outer part of their course. In 
several sections we see them just at the inner edge of the cortex, or rather of that 
outer zone of vortex which is alone preserved.* The bundles in this position are of 
considerable size, and may contain as many as twenty trachee. Their smaller 
elements are towards the exterior, and are spirally thickened, while the inner and 
larger trachez are scalariform, or at least their spiral band is more closely coiled. 
These facts can be made out where the section is oblique. We may infer then, that 
the xylem of the leaf-trace bundle was centripetal. 
The bundles which we meet with in the cortex are often larger than those which 
pass out into the whorl of bracts, and no doubt sometimes subdivided on their way 
through the outer cortical layers. 
* See Wintiamson, loc. cit., Part XVIII, Plate 27, fig. 3. They are also well shown, on a small 
scale, in our photograph 25, on Plate 76, 
