TRANSACTIONS OF SECTION C. 479 
when Brongniart separated the plants contained in the group into two divisions— 
one of which (Aguisétacées) he identified with the living Equisetums, and the 
other (Astérophyllitées) he regarded as being Gymnospermous Dicotyledons, To 
Schimper belongs the merit, as I believe it to be, of steadily resisting this 
division ; nevertheless, paleeobotanists are still separated into two schools on the 
subject; Renault, Grand-Eury, and Saporta adhere more or less closely to the 
Brongniartian idea, whilst the British and German paleontologists have always 
rejected the idea that any of these plants were other than Cryptogams, 
A fundamental feature of the entire group is seen in their foliar appendages, 
which, however morphologically and physiologically modified, are arranged in 
nodal verticils. This appears to be the only characteristic which the plants possess 
in common. 
Calamites and Calamodendron, In his ‘ Prodrome’ (1828), and in his later 
‘Vegetaux Fossiles, Brongniart adopted the former of these generic names as 
previously employed by Suckow, Schlotheim, Sternberg, and Artis. It was only 
in his ‘ Tableau des Genres de Vegetaux Fossiles’ (Dictionnaire universel d’ Histoire 
Naturelle, 1849) that he divided the genus, introducing the name of Calamodendron 
to represent what he believed to be the Gymnospermous division of the group. A 
long series of investigations, extending over many years, has convinced me that no 
such Gymnospermous type exists.‘ The same conclusion has more recently been 
arrived at by Vom c. M. D. Stur,? after studying many continental examples in 
which structure is preserved. What I regard as an error appears to have had an 
intelligible origin—the fertile source of similar errors in other groups. 
Nearly all the Calamitean fossils found in shales and sandstones consist of an 
inorganic, superficially fluted substance, coated over with a thin film of structure- 
less coal. (See Histoire des Végétaux Fossiles, Vol. i., Pl. 22), the latter being 
exactly moulded upon and retaining the outlines of the morganie fluted cast that 
underlies it, Brongniart and those who adopt his views, believe that the externai 
surface of this coal-film exactly represents the corresponding external surface of 
the original plant. Hence the conclusion was arrived at that the plant had a very 
large central fistular cavity, surrounded bya very thin layer of cellular and vascular 
tissues, as in some living Equisetums. On the other hand, Brongniart also 
obtained some specimens of what he primarily believed to be Calamites, in 
which the central pith was surrounded by a thick layer of vascular tissue arranged 
in radiating laminated wedges, separated by medullary rays. The Exogenous struc- 
ture of this vascular zone was too obvious to escape his practised eye. But, not 
supposing it possible that any Cryptogam could possess a cambium-layer and an 
Exogenous mode of development, Brongniart came to the conclusion that whilst the 
thin-walled specimens found in the shales and sandstones were true Equisetacee, 
those with the thick woody cylinders were Exogens of another type. His conclusion 
that they were Gymnosperms was a purely hypothetical one, justified by no one 
feature of their organisation. 
My researches, based upon a vast number of specimens of all sizes, from minute 
twigs, little more than the thirtieth of an inch in diameter, to thick stems at least 
thirteen inches across, soon led me to the conclusion that we have but one type of 
Calamite ; and that the differences which misled Brongniart are merely due to 
variations in the mode of their preservation.* It became clear to me that the 
outer surface of the coally film in the specimens preserved in the shales and sand- 
stones, did not represent the outer surface of the living plant, but was only a 
fractional remnant of the original carbon of that plant which had undergone a 
complete metamorphosis; the greater part of what primarily existed had dis- 
appeared, probably in a gaseous state; and the little that remained, displaying no 
organic structure, had been moulded upon the underlying inorganic cast of the 
medullary cavity. This cast is always fluted longitudinally and constricted trans- 
versely at intervals of varying lengths. Both these features were due to impres- 
sions made by the organism upon the inorganic sand or mud introduced into the 
1 Memoirs i. ix. and xii. “2 Zur Morphologie der Calamarien. 
2 Memoirs i. and ix. . 
