154 ON THE GENUS KNORRIA. 
truncate processes, supposed to be fleshy leaves, are present, but in 
the upper portion these are exhibited as long, slender processes, from 
two to three inches long. They are composed of the same amorphous 
sand which forms the stem itself, and are consequently casts proceeding 
from, and filled up through the stem. These processes are all free from 
the stem, being separated from it by a thin film of coal, and in con- 
sequence of this, the processes are broken off from the lower portion 
of the specimen. The whole stem is covered with a thin layer of coal, 
which separates it from the incrusting rock. 
In examining the structure of the stem of Lepidodendron we find, as 
already stated, that the woody cylinder is too slender to have formed 
the mould in which Kzorria was cast. The wood was surrounded by 
a cellular tissue of considerable thickness, and so delicate that it has 
never yet been seen preserved in anything like its entirety. It is 
generally replaced by some amorphous or crystalline substance, and its 
nature has been detected only by the occasional preservation of small 
portions, which have been protected by their neighbourhood to the 
woody cylinder, or to the outer sub-cortical layer. This outer layer is 
composed of small, regularly arranged, elongated cells. It appears to 
have been more durable than any of the other tissues, having resisted 
the decay which speedily destroyed the medulla, and the delicate cel- 
lular structure between it and the wood, and even the woody cylinder 
Which, from its relation to these two cellular structures, was probably 
more liable to decay. The specimens of erect Sigi/larie, discovered by 
Mr. Wünsch, in Arran, preserved erect in beds of volcanic ash, are com- 
pletely hollowed out; all the interior cellular and vascular tissue has 
disappeared, and only the layer of elongated cells and the outer cortical 
layer of indurated cells remain. This compact cylinder of elongated 
cells in Zepidodendron is penetrated in a spiral manner by the vascular 
bundles which pass to the leaves. These bundles are composed of a 
few scalariform vessels, surrounded by a considerable quantity of cel- 
lular tissue, of the same delicate structure as the inner layer which 
is always altogether, or almost altogether absent, and, like it also, it is 
very rarely preserved. 
This specimen then shows that Kzorria is a Lepidodendroid stem 
which, after being imbedded in mud or sand, lost by decay the whole 
of its interior up to the cylinder of elongated cells, and lost besides 
this, the vascular bundles with the accompanying cellular tissue which 
