494 
PROFESSOR W. C. WILLIAMSON ON THE ORGANIZATION 
medullary cavity alone having a diameter of 2 inches. I think this chain of facts jus- 
tifies me in my conclusion that the common Calamitean medullary casts owe their form 
to a vital process carried on during the life of the plant, and not to an inorganic decay 
of the pith-cells occurring after its death'*. 
Of the common instances in which we find the well-defined Calamite composed of 
shale or sandstone, and covered by a carbonaceous layer, we have now no difficulty in 
discovering an explanation. The medullary cavities, and in the case of the Ccdamopitus 
the verticillate radial canals also, have been filled up with inorganic matter which formed 
an exact cast of each cavity and canal. This cast, having become indurated, retained 
permanently the grooves and ridges impressed upon it by the inner surface of the woody 
zone; in the case of the Calamopitus there also projected more or less prominently from 
the surface of the cast the inorganic contents of the verticillate infranodal canals, which 
in their uncompressed condition would stand out from the central cast like spokes from 
the nave of a wheel. So long as the woody zone retained its integrity these conditions 
remained unchanged ; but pressure and chemical agencies gradually produced alterations. 
As the vegetable tissues of the plant became converted into coal, their structure dis- 
appeared along with much of the material composing them. And when the process was 
completed, what remained was deposited, as if by a process of electrotyping, in the form 
of a thin film of coal, moulded upon and taking the shape of the hardened central cast, 
* That the common specimens of Catamites were inorganic casts of the interior of the woody cylinder, occu- 
pying the cavity left by the disappearance of the pith, was suggested by Mr. Dawes ten years ago (“ Further 
Remarks upon the Catamites,” Proceedings of the Geological Society of London, vol. vii. 1851 ) ; though I had 
overlooked the circumstance until after the present memoir was read before the Royal Society. I arrived at my 
conclusions from independent evidence. But Mr. Dawes differs from me in adopting the idea of decay to account 
for the disappearance of the pith, the reverse of my opinion that it was the result of a vital process of absorp- 
tion. Transverse sections of sandstone Catamites exhibit a crenulated outline of geometric regularity ; and this 
outline recurs throughout the entire length of specimens from 6 to 8 feet long. I can scarcely conceive of inor- 
ganic decay producing so sharply defined and uniform a result. Had the woody zone been a continuous cylinder, 
whose inner walls were unbroken, such conditions might have occurred ; but this is not the case. As we have 
seen, it consists of a ring of detached wedges, separated from one another by radiating masses of cellular tissue, 
which latter are continuous with, and prolongations of, the pith. Now that the decay should not have extended 
along these prolongations (my primary medullary rays) but invariably have stopped at a crenulated line of which 
the tissues themselves afford no indication, is, to me, incredible. The uniformity of these results appears a suf- 
ficient proof of the correctness of my hypothesis. But there remains further evidence. In the case of Cala- 
mopitus we have to account for the infranodal canals. Whatever else these may have been, they were clearly 
outward prolongations of the central medullary cavity ; and if decay was the agent producing the latter, it must 
equally have produced the former. In other words, this capricious agent, dependent upon a variety of outward 
conditions, though it respected the cellular primary medullary rays as a whole, yet attacked each one of them 
at certain circumscribed points, arranged in regular verticils which recurred with most unvarying uniformity, 
immediately below each node, from one end of the stem to the other. I must confess myself unable to accept 
such an explanation. These infranodal canals obviously existed in the living plant, in which they fulfilled some 
unknown function. At the same time they are but prolongations of a central cavity which must have coexisted 
with them. I therefore conclude that the entire structure resulted from the operation of that vital force which 
works out its designs with unbroken regularity, respecting boundary lines of which the eye, even though aided 
by the microscope, can frequently detect no trace. — October 3rd, 1871. 
