﻿1851.] 



DAWES ON CALAMITE. 



197 



with whose researches he was not then acquainted, Mr. Dawes states 

 that, from the observations hitherto made, the Calamite appears to 

 consist of a large central column of tissue, surrounded by a cylinder 

 of woody structure. This central part, having commonly rotted 

 away soon after the death of the plant, has been replaced by a 

 mineral cast of the inside of the ligneous cylinder, and, owing to the 

 general disappearance of the latter, the jointed and ribbed cast is the 

 usual form in which the Calamite is presented to us in the carbo- 

 niferous rocks* . 



The outer ligneous surface appears also to have been ribbed, or 

 rather marked with longitudinal striae, more or less perfect, but with- 

 out any indications of joints or constrictions f ; the position, however, 

 of these articulations is shown upon some specimens by the presence 

 of small and somewhat oval verticillate leaf-scars, to which may have 

 been appended leaves, corresponding to those attached to Brongniart's 

 Calamites radiatus%. These leaf-scars were connected with the small 

 round or ovate processes, usually observed at the joints of the Cala- 

 mite-cast, by large muriform rays, which passed horizontally through 

 the outer cylinder of woody tissue. These processes have been for- 

 merly mistaken for the true leaf-scars of the plant §. 



This outer woody layer is usually met with only in a carbonized 

 state, — that is, in the shape of a thin coating of crystalline coal || ; 

 but occasionally the structure has been met with well-preserved. It 

 is composed of two distinct tissues, the one cellular, the other pseudo- 

 vascular. In the transverse section these appear to be arranged in 

 alternating vertical plates, which radiate from the inner aspect of this 

 cylindrical woody layer to its periphery, and correspond with the ribs 

 and furrows seen on the surface of the interior cast. These alterna- 

 ting plates, being of different shades of colour, are sufficiently visible 

 to the unassisted eye^f. 



The darker stripes, which constitute the pseudo-vascular part of 

 the structure, arise in somewhat wedge-shaped masses from the centre 

 of each furrow, and as this tissue diverges into the cellular part of the 



* This fact was first distinctly shown by Germar in 1838, and in the same year 

 by Corda, who pointed out that, in all probability, the stem was not originally hol- 

 low, but occupied by cellular tissue, which had subsequently altogether rotted out. 



f This condition is seen in Unger's figures, published in the German transla- 

 tion of Petzholdt's work ' De Calamitis et Lithanthracibus.' It is also well shown 

 upon specimens in the author's collection. 



% Hist. Veg. Foss. pi. 26. figs. 1, 2. 



§ Brongniart considered these processes to be simple tubercles, which had 

 never been connected with any leafy or other appendage. 



|| Brongniart had, as early as 1828, observed specimens having this outer cover- 

 ing in a carbonized state ; he also remarked that the ribbing was very indistinct, 

 and that the articulations or joints were to be observed only beneath the coaly 

 covering. So long as this outer covering had been met with only in the carbo- 

 nized state, there was no proof, as Lindley and Hutton justly observed, ' Fossil 

 Flora/ vol. L p. xxx, that the coaly matter, thus found enveloping these fossils, 

 was really the remains of a cortical integument, or formed any part of the original 

 organization of the stem, for it might have been an independent carbonaceous 

 formation. 



% This arrangement of the tissues was regarded by Cotta as indicating medul- 

 lary rays, which opinion Unger considered to be incorrect. 



