164 
On the History, Histological Structure, 
botanical skill of Mr. Oarruthers, however, renders it important to 
state his views in the present imperfect state of our knowledge of 
this truly wonderful plant.” 
I will recur to this note again, and will only now stop to say 
that nothing of any importance is added in this last publication, as 
is evident from the specific characters, which it will be noticed 
scarcely differ from those which were given in the original paper ; 
and where they differ it is only to commit Dr. Dawson more com- 
pletely to error. The diagnosis is as follows: — “Woody and 
branching trunks, with concentric rings of growth and medullary 
rays. Cells of pleurenchyma not in regular fines, cylindrical, thick- 
walled, with a double series of spiral fibres. Disks or bordered 
pores few, circular, and indistinct. The specimens are usually 
sificified, and the bark in a coaly state.”* 
It is necessary to say that my descriptions are made from a 
specimen given me by Dr. Dawson, for the purpose of having it 
prepared for microscopical inspection. It is in the condition winch 
he thus describes : — “ The wood appears as a homogeneous black 
cherty mass, only faintly marked with a longitudinal striation 
parallel to the fibres. It presents its structures in a perfection un- 
surpassed by any fossil wood known to me.” 
The large and fighter-coloured fossils referred to by Dr. Dawson, 
and specimens of which he presented to the British Museum, have 
also been sliced. In one of them the tissue is entirely made up of 
spherical cells; and this appearance is not due to concretionary 
action, but to the limits of the cells, the walls of which can still be 
detected. In other specimens the spherical structure is due, as 
Dr. Dawson says, to concretionary action. The largest of these 
specimens contained an irregular-shaped cavity, which was filled 
with minute free double-headed prisms of quartz. I shall, however, 
dismiss these specimens from consideration, and confine my attention 
to that on which Principal Dawson’s histological investigation of 
the plant is based. 
Under a low power a transverse section exhibits a somewhat 
loosely aggregated mass of circular openings of nearly uniform size, 
except that there are recurring tracts of smaller and more closely 
aggregated openings. These tracts have a concentric arrangement, 
and are the rings of growth of Dr. Dawson (Plate XXXI., Fig. a). 
On submitting the specimen to a higher power, we find that the 
circular openings have well-defined walls of considerable thickness, 
and that they are nearly uniform in size, except where the tracts of 
small diameters occur to which I have referred (Plate XXXI., Fig. c). 
It is obvious that all these openings represent the same kind of 
tissue, that is, as far as they are concerned, the structure is perfectly 
uniform and simple. We further observe that, while the majority 
are cut transversely, some are cut more or less obliquely, showing 
* 1 Pre-carboniferous Plants,’ p. 1C. 
