OF THE FOSSIL PLANTS OF THE COAL-MEASURES. 
495 
whilst the corresponding casts of the infranodal canals, unable to hear the pressure to 
which they were subjected, were forced down upon the medullary cast, on the surface 
of which they now appeared as very slightly elevated tubercles. The effect of these 
changes was the more or less complete reproduction, on the exterior of the carbonaceous 
layer, of forms which really belonged only to its interior , a reproduction which has 
occasioned much of the existing misapprehension respecting these fossils. Had the 
longitudinal ridges and furrows seen on the exterior surface of the carbonaceous film 
belonged to the corresponding portion of the living plant, they would have alternated 
with those of the medullary cast, as is shown by the restored diagram (fig. 1). But this 
is very rarely the case. Hence I cannot avoid the conclusion that external markings 
afford no absolute clue to the real nature of the external surface either of the bark or 
of the woody zone of the living Calamite. I have referred to the scars or tubercles so 
frequently seen on the medullary casts of Calamites ; these are always arranged in 
verticils. The scar is sometimes circular, at others oblong, but always planted on the 
upper extremity of each vertical ridge, immediately below each node. The common 
aspect of the round variety is shown in Plate XXVII. fig. 27, and the oblong one in fig. 28. 
In both figures l represents the scars in question, i the node, e the inner angle of each 
woody wedge, and c the broad inner surface of each primary medullary ray. These scars 
are usually a little raised above the surface of the ridge upon which they are planted, but 
not invariably so. They, as I have already intimated, are the remains of the infranodal 
canals ; and the degree of prominence which the scars exhibit has partly depended upon 
the extent to which inorganic matter has penetrated the interiors of the original canals, 
and partly on the chemical changes which the woody cylinder, through which these 
canals passed, has undergone. In the specimen of Calamopitus figured in the 4th edition 
of Lyell’s ‘Manual of Elementary Geology’ (fig. 478), as well as in my memoir on 
Calamopitus (fig. 1), we see that in the sandstone casts these scars are merely the bases 
or remnants of what that fine specimen exhibits so perfectly, viz. a verticil of radiating 
projections, each more than A of an inch in length, and exactly resembling the spokes of 
a wheel, of which the central medullary cast is the nave. This specimen demonstrates 
that the common conditions seen in figs. 27 & 28 are very deceptive ones, which would 
inevitably mislead a student who had seen no other form ; but read in the light afforded 
by the specimen above referred to, and of those represented in figs. 22, 23 & 25, their 
history becomes simple enough. 
Before quitting the common forms of these internal casts I would call attention to a 
feature which I have noticed in several specimens, but of which I have as yet discovered 
no explanation. Plate XXVII. fig. 29 represents four internodes of a very long Cala- 
mite in the Cabinet of Mr. Wilde, of Glodwick Collieries, Oldham. The drawing is of 
the natural size. In the two lowermost internodes (k, k ), and to a large extent in the 
uppermost one (P), the longitudinal grooves are regularly parallel with each other and, 
like the internodes themselves, uniform in size; but in the shorter internode ( lb ) this is 
not the case. Plate XXVII. fig. 30 represents a few of the ridges and furrows of the 
latter enlarged about three diameters. Some of them are much thicker at one end than 
3 y 2 
