OF THE FOSSIL PLANTS OF THE COAL-MEASURES. 
285 
zone increases in thickness, enabling them still to maintain their connexion with the 
bases of the leaves that remain attached to the growing stem, 
M. Renault represents the first of his Sigillarian types by the Sigillana vascularis 
of Mr. Binney, but which is really a state of the common Lepidodendron selagmoides. 
When M. Renault denies that a Lepidodendroid state of this supposed Sigillarian 
plant exists, he overlooks the fact that Mr. Binney long ago described and figured a 
partially decorticated specimen in this condition under the name of Lepidodendron 
vasculare .* In that memoir Mr. Binney correctly points out that the plant only 
differs from his Sigillana vascularis in the absence from the former of an exogenous 
zone. 
Fig. 1 represents a transverse section of a branch of this plant, enlarged about 
13 diameters, its actual diameter in the longer direction being nearly ‘8. In its 
centre is the vasculo-medullary axis, a, the periphery of which consists of a continuous 
zone, sharply defined externally, composed of numerous barred vessels. More intern¬ 
ally, cellular elements are interposed between these clusters of vessels, until, in the 
central portion of the axis, the vessels are either isolated or combined in very small 
groups. The medullary cells are of two kinds, as pointed out in my memoir, Part II., 
Plate 24, fig. 3. The barred or reticulate character of many of these cells affords an 
infallible guide to the identification of this plant. 
Fig. 2 represents a segment of the only specimen I have seen in which all the cortical 
tissues are preserved; for this specimen I am indebted to Mr. Cash, of Halifax. At 
a we have the periphery of the vascidar zone. At b is the innermost cortex, separable 
into three parts—an internal zone, 6, consisting of very minute cells ; a middle area, 
b', in which the cells are of larger size ; and an outer one, b", in which they exhibit a 
tendency towards a cyclical arrangement. In this zone the foliar vascular bundles, c, 
are invariably intersected, in these transverse sections, at right angles to them vertical 
course. Enclosing this endophloem we have a middle cortical layer, d, which is very 
rarely preserved, its jfface being usually vacant, as in fig. 1 , d. This zone consists of 
very delicate parenchyma, the cells of which at its inner margin, d', exhibit a disposi¬ 
tion towards a radial arrangement. The vascular bundles pass through this zone in 
an oblique direction. The yet more external zone, e, is almost invariably preserved in 
these young branches. It consists of strongly-defined thick-walled cells, which 
diminish in size from within outwards—the compressed aspect of those shown at 
fig. 2, e', being obviously accidental. The smaller peripheral cells gradually pass into 
crescentic clusters of radially disposed prosenchymatous cells, f Fig. 1 demonstrates 
that these prosenchymatous or bast tissues are first developed in the convex outward 
extensions of this portion of the bark which underlie the several leaves. The latter 
organs, composed of coarse parenchyma, are seen at g, g'. At g' is the single foliar 
bundle; in each of the three leaves of fig. 1 in which this bundle appears there are 
‘ Quarterly Journal of tlie Geological Society of London,’ May, 1862, p. 110, plate 6. 
2 p 2 
