322 
PROFESSOR W. WILLIAMSON ON THE ORGANIZATION 
as in any other exogenous plant, yet we know of no gymnospermous stems that are 
entirely composed of such vessels, but which are so characteristic of the true 
carboniferous Cryptogams, hence I am inclined to place ■ Astromyelon in the 
Cryptogamic group. 
The plant just described is the only one belonging to a distinct type of vegetation 
left unnoticed in my previous memoirs. But since the earlier parts were published 
numerous objects have come under my observation throwing additional light upon 
several of the genera which I have previously described. These I now propose to 
examine in detail. 
Catamites. 
The wide-spread interest which these plants excite, and the continued existence of 
two sharply-defined and very discordant views respecting their nature and affinities, 
render further investigations necessary. Since my first memoir, which mainly treated 
of these objects, was published, I have gathered numerous additional illustrations of 
their history. The study of these specimens has only confirmed my previously 
expressed conclusion, that we possess but one type of these plants, and that the 
separation of Calamites from Calamodendron has no foundation in the facts of their 
organization. Fig. 8 is a transverse section of a small stem or twig not much more 
than ’033 in diameter. The medullary cells (b) are here unruptured, the medullary 
fistular cavity having as yet no existence. Nine longitudinal internodal canals are 
seen (e) , and these form the only recognizable line of demarcation between the 
pith, b, and the bark, h. There is but little difference observable between the cells 
of these two structures. 
Fig. 9 is obviously a decorticated specimen, similar in all other respects to fig. 8, 
but with eight canals, and the section has passed through the stem rather obliquely. 
In fig. 10 we have a transverse section through a similar stem or branch to fig. 8. 
We still d iscover the bark, h, the internodal canals, e, again nine in number, and the 
medullary parenchyma ; but the bark, in this example, is a thick layer of parenchyma 
of coarser tissue than that composing the medulla, and the latter now displays a 
central fissure, a, winch obviously indicates the commencement of the formation of the 
medullary fistular cavity. We have still but very slight indications of the formation 
of woody wedges external to each of the internodal canals. Fig. 11 is a decorticated 
example in the same stage of development as fig. 10, only the medullary fistular 
cavity, a, is now of large size, and the internodal canals, e, are eighteen in number. 
Fig. 12, on the other hand, is another decorticated example in which the canals, e, are 
eleven in number, and the vascular wedges, f are now advanced in development ; 
but the central fistular cavity, a, is in a stage of development intermediate between 
that of fig. 10 and fig. 11. In fig. 13, the original of which was found by 
Mr. Butterworth, the stem has attained to larger dimensions, being now about 
•12 in diameter. The layer of medullary cells, b, Is now extremely scanty, whilst 
