74 Professor Harkness on Coal. 
are so undecided, that although I should be inclined to consider them 
indicative of a monocotyledonous plant, I shall not venture at any 
conjecture respecting them.’’? The structure which the Lancashire 
cannel usually presents is that figured by this author, and many of 
the Scotch parrots afford the sameappearances when sliced and mag- 
nified. But there is one circumstance to be considered which mili- 
tates strongly against the idea that this can be regarded as true 
vegetable tissue, and this is, that among the many plants which 
have been met with in the coallields, retaining internal structure, 
none of these furnish us with tissue bearing any affinity to this 
structure as generally seen in cannel. The structure, as above 
referred to, appears to me to be merely the results of struc- 
ture, and not what is or was regarded by Witham. merely 
monocotyledonous tissue. From an examination of many can- 
nels, I am inclined to regard the circular spaces figured as 
having originated in the decomposition and total destruction 
of the vascular sheaths of minute rootlets of stigmaria, which 
have totally disappeared, leaving in the centre of these a 
small portion of black coaly matter, the remains of that 
portion of the cellular tissue which represented the pith, and sur- 
rounded by other coaly matter, the remains of the external cellular 
portion. Such a conclusion would lead to the inference, that the 
vascular sheaths sooner became subject to change, and were separated 
from the plants of which they originally formed a portion—a cir- 
cumstance which we shall find other phenomena afforded by coal tends 
to show was the case. From what has already been said concern- 
ing the nature of the vegetable tissue which occupies so large a por- 
tion of the plants forming coal, we should be induced to infer that, 
when their substance retains structure, this would be present in the 
form of cellular tissue; and such is really the case with such of the 
Scotch cannels as are most hydrogenous, and have been subjected to 
the smallest amount of compression and chemical alteration. Where 
the amount of chemical change has been considerable, as in the 
ordinary Scotch and Lancashire cannels, the cellular tissue has dis- 
appeared, and nothing remains to show the original structure of the 
vegetation from whence coal has been derived, save the hollow cylin- 
ders from whence the vascular portion of the plants have escaped ; 
but even in this case, the vegetable matter has been in such a con- 
dition as to resist the compression which would otherwise have obli- 
terated these cylinders, as is the case in ordinary coal, which has: 
undergone the greatest amount of chemical change and compression, 
and which, in general, has, in consequence thereof, lost all traces. 
of the original structure of the plants which compose it. 
Besides the cellular tissue, the remains of which can be detected 
in the least altered Scotch cannels, we, in some instances, meet with 
the vascular tissue manifesting itself in coal. When this is the case, 
this vascular tissue does not occur in the cylindrical form which it 
