OF THE FOSSIL PLANTS OF THE COAL-MEASURES. 
353 
to some mineralization of them, I am unable to determine. It is needless to point 
out how much fig. 91 resembles the ordinary aspect of a radial section of a wood 
with the mural cells of its medullary rays crossing the vessels at right angles to 
the vertical course of the latter. 
The only stems which I have examined that bear any resemblance to the one now 
described are those of Lyginodendron Oldhamium, illustrated in my fourth memoir, 
and in which the medullary rays are of unusual size ; but in that plant the vertical 
length of each ray, as seen in tangential sections, many times exceeds its breadth. 
This is not the case with the plant under consideration. Though opposed as a rule 
to giving names to detached fragments of wood, this one appears to have such 
remarkably distinctive features, that I venture to designate it Lyginodendron 
anomalum. It may be remembered that the late Mr. Gouklie described casts of 
the bark of a Lyginodendron from the Scotch carboniferous deposits. It will be an 
interesting fact if the specimens now described prove to belong to the woody zone 
of Mr. Gourlie’s plant. Should they do so, the genus Lyginodendron will be 
characterized by the possession of a most distinctive internal organization. 
The Oldham calcareous nodules very frequently contain fragments of wood of various 
kinds, which, on examination, often prove to be masses of cortical cellular tissue. A 
very large fragment of this kind was found by Mr. Nield, to whom I am indebted 
for the specimen from which the sections that I am about to describe were made. The 
entire fragment is about 3^ inches in diameter from its medullary to its peripheral 
surfaces. At its inner portion it consists of parenchyma, the cells of which are not 
arranged in any regular order. Their transverse diameter (fig. 96) is about ’01, whilst 
they are a little elongated vertically, many of them having a diameter, in that direction, 
of ‘02 (fig. 97). In these vertical sections many of the cells exhibit clear evidences 
of their meristem origin in the secondary, but perfected, divisions seen within many 
of the older cells (fig. 97, a, a). Proceeding from within outwards, we soon find, in 
transverse sections, that these cells tend to arrange themselves in radial lines (fig. 93a) 
whilst radial vertical sections (fig. 94) show that as they do this, the cells increase in 
vertical length, and then- longer sides approach more and more to perfect parallelism 
with each other. But in addition to this parallelism, the cells display a disposition to 
group themselves in well-defined clusters, each cluster being longer in the radial than 
in the vertical direction. This arrangement, as is seen in fig. 94, a, continues to prevail 
until we reach the peripheral margin, b, of the specimen. No signs of this peculiar 
grouping appear in transverse sections of this part of the specimen where, at about an 
inch from the inner or medullary surface of this bark, we obtain the condition represented 
in fig. 98, which is part of a transverse section, and in fig. 99, which is a tangential one 
of the same part. The whole tissue has now assumed a prosenchymatous character, the 
cells being arranged in very regular and uniform radiating lines proceeding from within 
outwards. These cells now have a transverse diameter of about '0041 to '0027, whilst 
many of them are '025 in length ; fig. 93, a, exhibits their collective aspect in transverse 
2 z 2 
