158 PROCEEDINGS OF XHE GEOLOGICAL SGCIBTT. 



have served the purpose of a rhizoma*. The best example that I 

 have seen of the rhizoma of a Calamite is that figured in Plato IX. 

 (fig. 21), from a specimen presented by me to the Geological Society 

 many years ago. 



"With regard to Calamodendron the difficulties are greater, and 

 have been well stated by Prof. "Williamson in a recent paper in the 

 ' Memoirs of the Literary and Philosphical Society of Manchester 'f, 

 in which he describes under the generic name Galamopitus a peculiar 

 stem, which, while he identifies it in its general characters with 

 Calamites, he justly regards as being in internal structure distinct 

 from the Calamodendra described by Cotta and Binney. 



The characters of Calamodendron as distinguished from ordinary 

 Calamites may be summed up as follows : — 



(a) The part usually preserved is the internal axis, corresponding 

 to a Sternbergia. It presents ribs similar to those of Calamites, but 

 more angular, and almost always having traces of woody fibres capa- 

 ble of showing the structure on some part of their surface. I have 

 not seen on these casts any distinct traces of scars or areoles. These 

 casts of the pith of Calamodendron constitute the greater part, if not 

 the whole of the specimens referred to G. approocimatus. 



(h) More complete specimens are invested with woody matter, 

 arranged in wedges, and consisting of elongated cells and porous, 

 discigerous, or pseudo-scalariform tissue. My specimens do not 

 show distinctly the arrangement of these ; but this has been well 

 described by other observers. Williamson describes meduUary rays 

 in the woody bundles in addition to the large cellular tracts inter- 

 vening between them. 



(c) The actual external surface of Calamodendron is not certainly 

 known ; but I have been disposed to regard as of this kind those 

 ribbed stems, found in the coal-formation, which have swollen nodes 

 as if caused by the emission of whorls of small branches. I have 

 specimens of these in my collection, which I have hesitated to name 

 or describe until they could be better understood. Prof. "Williamson's 

 description of Calamopitus now inclines me to suppose that they be- 

 long to that genus or to allied forms. 



"With regard to the affinities of the Calamodendra, the structure of 

 the stem raises them above the Calamites and modern Equiseta, and 

 justifies the conjecture of Brongniart that they may have been gymno- 

 sperms. "Williamson, Carruthers, and Binney, however, attribute to 

 them a cryptogamous fructification. In this case they may, as the 

 former suggests, be a connecting link between Acrogens and Gymno- 

 sperms. Should subsequent investigations confirm this view, it will 

 throw an interesting light on the possible affinities of Sigillaria. 

 Calamites, on the one hand, and Lepidodendron on the other, are 

 distinctly cryptogamous and are related to, or included in, the mo- 

 dern families of Equisetaceas and Lycopodiacese. But Calamodendron 

 seems to form a connecting link between Calamites and the ribbed 

 Sigillarice ; and in like manner Lepidopldoios seems to connect the 



* See my description in Quart. Journ. Geol. Soc. vol. x, 

 t Vol. iv. 3rd Series. 



