264 PROF. W. C. WILLIAMSON ON THE 



rays. Now this very complicated arrangement of parts 

 is admitted by all to exist alike in Calamites and Cala- 

 modendron, and the inorganic cast of the interior of the 

 medullary cavity of a Calamite also reappears unchanged 

 in the Calamodendron. This remarkably detailed iden- 

 tity in the morphological features of two plants^ the former 

 of which is admitted to be a Cryptogam, whilst the latter 

 is assumed to be an Gymnospermous Phanerogam, is, in 

 itself, sufficient to suggest the strongest doubt as to the 

 accuracy of this assumption ; but fig. 3 carries us further. 

 Abundance of specimens in my cabinet prove the absence 

 from the bark of all the nodal constrictions, as also of 

 the longitudinal ridges and furrows, formerly supposed 

 to be characteristic of the exterior of the bark of a 

 true Cryptogamic Calamite. We possess little evidence 

 respecting the bark of Calamodendron, but M. Brongniart 

 inclined to the belief that it also had a smooth exterior. 



There being such a remarkable identity in the general, 

 as well as in the minute morphology of Calamites and 

 Calamodendron, let us now see what value may be assigned 

 to the differences of detail that are supposed to distinguish 

 the two plants. 



To facilitate an apprehension of this part of the subject, 

 I have prepared diagrammatic outlines of three cubical 

 wedges. One of these (fig. 4) is cut out of the stem of 

 a Calamite, fig. 5 is from my so-called Calamopitus, and 

 fig. 6 is from a Calamodendron from Chemnitz. Each 

 of these blocks comprehends superiorly, a portion of the 

 horizontal transverse section, and inferiorly, of a vertical 

 tangential section. In like manner in each block the two 

 outer portions, g, g, represent two primary medullary rays, 

 and the central area, c, is part of a single vascular wedge. 

 In each of these figures the further margin, c, of each cube 

 is supposed to be the portion nearest to the medulla. 



