OF THE FOSSIL PLANTS OF THE COAL-MEASURES. 
351 
cellular bundle- sheath and the outer cortical layer is indicated by a rather irregular 
ring of cells, a, which have had some peculiar cell- walls, giving them a darker hue than 
the rest of the section. Fig. 84 represents a segment of fig. 82, also enlarged to 140 
diameters. In it the tendency of the inner cells of the cortical layer b, to arrange them- 
selves in concentric circles is very marked ; also the disposition of the innermost ones 
to become compressed and narrowed in the radial direction. The bundle-sheath in this 
specimen has disappeared. Fig. 86 is a portion of a longitudinal section enlarged 60 
diameters ; the vascular bundle is seen to consist of barred vessels. The bundle- 
sheath, a, is composed of very narrow, vertically elongated, square-ended cells, whilst 
in the cortex, b, the cells are of larger size, of coarser texture, and exhibit a strong 
tendency to become prosenchymatous. Fig. 87 is a transverse section of a stem like 
fig. 80, but giving off a long, straight, lateral branch. In this section the large and 
small vessels of the central bundle are more irregularly intermingled than is the case in 
fig. 80. On the whole the largest vessels are found at the periphery of the bundle. 
Judging from the size of its vessels and from its average diameter I presume that a 
transverse section of this branch would be intermediate between figs. 82 and 83. The 
section fig. 87, exhibits an extension of the bundle-sheath, a, of the central stem pro- 
longed outwards to form the bundle- sheath, a, of the branch, and the cortical layer, b, is 
similarly extended, b'. The connexion of the vessels of the branch with those of the 
central axis is not seen, owing to the slight angle at which the former have been given 
off from the latter, and which has prevented their direction from corresponding exactly 
with the plane of the section. Fig. 88 is a transverse section of another stem which 
exhibits the general features of those just described, but which differs from them in 
the small size of its central vascular bundle and bundle-sheath, contrasted with the 
diameter of its cortical outer layer. It is giving off a lateral branch, a, which is 
obviously ascending almost parallel to the main axis. The difference between the 
size of the vascular axis of the branch and that of the main stem is much less than 
in fig. 87. Still since this section occurs in the same slide as those represented in 
figs. 80-87, and since the same slide contains other sections which seem somewhat 
intermediate between the two extreme modifications, I am disposed to regard them all 
as belonging to the same plant. The differences between them are not greater than 
exist in similar sections of the aerial and subterranean stems of Psilotum triquetrum, 
to which the entire series of sections of this plant, displays a considerable resemblance. 
Three possibilities suggest themselves as to the affinities of this plant. It may be 
a fern stem, though I know no recent type of fern which it resembles ; it may be the 
root of some type of fern, an idea suggested by the tendency to a concentric arrange- 
ment of the cortical cells ; or it may belong to some dwarf type of Lycopodiaceous 
plants. For the present these points must remain undetermined. Meanwhile I would 
distinguish the plant by the temporary name of Rachiopteris cylindrica. I have not 
seen this form in the Oldham nodules. All the specimens figured are in a slide from 
the cabinet of Mr. Binns. 
2 z 
MDCCCLXXVIII. 
