﻿1851.] 



DAWES ON CALAMITE. 



199 



from the imperfect state of the specimens, to have been composed of 

 lax cellular tissue, traversed by pseudo-vascular bundles, and to have 

 been interrupted, at intervals corresponding to the joints, by hori- 

 zontal plates of tissue (Phragmata), the horizontal striae or radii upon 

 which correspond with the ribbing upon the cast. These Phragmata 

 usually present a larger or smaller ring at the centre *, as though per- 

 forated by a woody axisf. The author has in fact specimens of what 

 he believes to represent this axis, which appears to have been tra- 

 versed by a central cellular tissue, the true medulla of the plant. 

 The wood of this axis also exhibits a reticulate structure, similar to 

 that of Pinites. 



With regard to the structural analogies that have been stated to 

 exist between Catamites and Equisetum, the author remarks that the 

 presumed existence of tubular passages, similar to the aerial canals of 

 Equiseta, demand a short notice. Petzholdt considered that the sec- 

 tions of some specimens he had examined, and which retained the 

 remains of a carbonized woody structure, afforded evidence of two 

 sets of aerial canals, similar to those observed in transverse sections 

 of the stem of Equiseta. Mr. Dawes, however, observes, that both 

 the roundish and triangular spaces, referred to and figured by Petz- 

 holdt, are evidently the result of the decay of the parenchymatous 

 tissue and a bulging of the vascular plates, the regular arrangement 

 of which gave rise to a more or less regular series of these accidental 

 spaces, as seen in the transverse sections of the stem J. 



In conclusion, the author observes, that there are still many doubt- 

 ful points in the structure of these interesting fossils which can only 

 be cleared up by the discovery of more perfect specimens ; he consi- 

 ders, however, that although the Calamite appears to have had no 

 structure that can in any way unite it with the Equisetacece, never- 

 theless some portions of its tissues must be considered as having Acro- 

 genous characters ; whilst the rectangular cells of at least a part of 

 the parenchymatous tissue, being arranged in perpendicular series, 

 is a character more commonly met with in Endogens ; and, at the 

 same time, there is sufficient evidence of Gymnospermous affinities, 

 together with the presence of well-defined concentric rings, so charac- 

 teristic both of this family and of other Exogens. 



* This appearance is seen in the specimen figured under the name of Calamitea 

 bistriata (see Die Dendrolithen in Beziehung, &c, Taf. 15), which evidently re- 

 presents merely a Phragma of the plant, and not the woody structure, as Cotta 

 had supposed it to be. 



f The probability of the existence, of such an axis was, the author observes, 

 suggested by Dr. Petzholdt. 



X The specimens described by Dr. Petzholdt were met with at Gittersee, near 

 Dresden. They seem to have been much distorted, and the woody cylinder is 

 described as being in a carbonized state, and appears to have exhibited very im- 

 perfect traces of structure. 



