OF TILE FOSSIL PLANTS OF THE COAL-MEASUEES. 
489 
more marked than in any other specimen that I have examined. It will also be observed 
that, as in tig. 15, the transverse section exhibits little or no difference between the sections 
of the vessels of the woody layer and the cells of the primary medullary rays. 
Plate XXVI. tig. 21 represents a fragment taken from the upper part of tig. 19, oppo- 
site to the small star, and which is in the highest degree instructive : in addition to the 
transverse section, this specimen exhibits, at its inferior half, the free longitudinal surface 
of the fossil running at right angles to the section, a is part of the central fistular cavity 
filled with dark ironstone, b is the cellular pith corresponding with fig. 20, h ; and in like 
manner the crenulated line#, x corresponds with the similar line in fig. 20. In the left- 
hand portion the woody zone is retained in situ; but to the right this has been detached 
from the pith (5), the separation taking place at a vertical surface corresponding with 
the crenulated line x, x, and leaving behind it a fluted surface identical in every respect 
with that of the ordinary Calamites with which we have so long been familiar. The 
sharply defined longitudinal grooves (V, e'), separating the concave ridges, are clearly seen 
to be identical in position with the longitudinal canals ( e ) ; whilst the prominent ridges 
(f, f), or exteriors of the woody wedges, occupy a position more peripheral, but radially 
vertical to that of the parallel grooves (e 1 ) — arrangements which throw a flood of light 
upon the ordinary structureless examples of Calamites. 
Plate XXVI. fig. 22 is a tangential section of this specimen made in the plane of the 
longitudinal canals, or a little more internal than the crenulated line (figs. 20 & 21, #, x) ; 
but since the section fortunately crosses a node at the line i, i, we obtain evidence that the 
arrangement of the vertical canals ( e , e ) at this portion of the plant differs from what exists 
in the types previously described. Instead of terminating near the node as cul-de-sacs, 
in the present example they enlarge into triangular spaces, and then, dividing right and 
left, they pass downwards to form the canals of the internode next below*. The cells 
of the pith describe at this point a series of Homan arches (b\ //), which form the inferior 
boundaries of the canals at their bifurcation ; the rest of the section is principally occu- 
pied by the ordinary parenchymatous medullary cells, as they present themselves opposite 
to the primary medullary rays, though here and there a few bundles of barred vessels 
demonstrate that it has dipped into the woody zone. This is especially the case at the 
node and near the centre of the specimen, where an elliptical figure bounded by vessels 
marks the position of a young branch such as is represented in fig. 13. But the section 
under consideration reveals some other important features. Within and below each of 
the Roman arches ( b ', V) we observe that the cellular tissue is ruptured longitudinally 
for a short space. In some instances this rupture (/, l ) is so slight as to be scarcely 
appreciable, and might indeed have been deemed accidental but from its constant rela- 
tions to some other features yet to be considered. 
In Plate XXV. figs. 23 & 24 we have two radial longitudinal sections, both of them 
being so made that the superior half of each above the node ( ii ) has passed vertically 
* In fig. 37 we have another radial section which intersects one of the horizontal portions of a canal (c) 
passing from one triangular space to another. 
