OF THE EOSSIL PLAINTS OF THE COAL-MEASURES. 
487 
The type which I have thus described in detail appears to be the one occurring most 
abundantly in the Lancashire Coal-measures; but along with it some others occasionally 
occur, which may have a specific value, though its exact amount is difficult to determine, 
since they are most of them rare, and of some only single examples have yet been found. 
Plate XXIY. fig. 14 represents one of those, of which I have seen several specimens. 
The entire diameter of the decorticated stem is - 21. Each woody wedge contains from six 
to eight laminae (</), separated by strongly marked secondary medullary rays (cl). Each 
of the principal laminae consists of a linear series of from nine to twelve vessels, which 
are remarkable for their large size. We have already seen that the largest vessels usually 
found in the type already described, range from ‘003 to *006, whilst near the longitu- 
dinal canal they are generally much smaller; but in this instance the vessels are as 
much as ‘01 in diameter. The specimen also illustrates very clearly the intercalation of 
additional laminae, as at g\ g". The cells of the pith are smaller than usual, and those 
of the primary medullary rays ( c ) especially so. Not having a longitudinal section of 
the specimen, I am unable to determine whether the small structures intervening between 
the inner extremities of the vascular laminae (g) and the longitudinal canals (e) are mi- 
nute vessels or elongated cells. The specimen thus possesses a marked individuality, 
though I am at present unable to determine whether it represents a state or a species. 
Plate XXIV. fig. 15 represents an example of which we have both the longitudinal and 
transverse sections, both of which are very distinct in their peculiarities. The specimen 
is decorticated, and has a diameter of -25. The exterior of its woody cylinder has been 
almost smooth, exhibiting none of the usual flutings arising from the prominence of the 
woody wedges (f). Indeed in the transverse section it is impossible to say where the 
woody laminse terminate, and the cellular tissues of the primary medullary layers begin. 
The medullary cells (b) are remarkably large, and the canals (e) also rather larger than 
usual ; but the vessels and the cells of the primary medullary rays are not more than 
*0025 of an inch in diameter. The suddenness with which the large medullary cells 
contract to form the small cells of the primary medullary rays constitutes a striking- 
feature of the plant, the general aspect of which is almost exactly the opposite of the 
one last described in every respect. 
Fig. 16 represents the medullary extremities of one of the woody wedges (f), and two 
of the primary medullary rays of another variety possessing great beauty. The woody 
laminae are very regular, and the intervening secondary medullary rays very distinct, 
whilst the manner in which the irregular parenchyma of the medulla (b) passes into the 
linear arrangements of the primary medullary rays (c) is very clearly shown. But the 
most remarkable feature of the specimen is the entire absence, from the apex of every 
one of the woody wedges, of the longitudinal canal. I at first thought that the section 
might have traversed a node into which the canals did not extend ; but I am convinced 
that such was not the case. The place of the canal is occupied by firm, strong-walled 
cells. I think it probable that the example of which a xylograph is given by Mr. 
Binney in his work (p. 20), and which led Dr. Hooker to surmise that the canals had 
