﻿198 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. [Mar. 12, 



stem, a small portion of the parenchyma opposite each adjoining rib 

 is usually left unpenetrated by the vascular fibre*. The lighter- 

 coloured stripes are in fact merely portions of the cellular or paren- 

 chymatous structure which have not been so closely interwoven with 

 the pseudo-vascular tissue, emanating from the furrows as before 

 mentioned. 



The darker-coloured tissue, when examined in the vertical section, 

 is found to be marked with fine transverse strice. This differs, how- 

 ever, from true scalariform structure, inasmuch as these peculiar 

 markings, like the areola on the walls of the vascular tissues of the 

 Coniferce, are only to be detected when the sections are cut in the 

 direction of the rays. Indeed these transverse striae in some speci- 

 mens are seen to become reticulate, as in the Pinites of the Coal- 

 measures. Moreover, in a transverse section, the wood of the Cala- 

 mite exhibits a network of quadrangular tissue, similar to what we 

 observe in the Coniferce. 



The lighter-coloured tissue appears to be composed of elongated 

 rectangular cells, exhibiting a general uniformity of sizef, and, as 

 these cells occur in nearly perpendicular and parallel rows, the ter- 

 minal junctions of the cells, owing to this arrangement, give to the 

 vertical slices, when the specimen is somewhat opaque, an appear- 

 ance as though lines of tissue passed horizontally through the struc- 

 ture J. If, however, as the author observes, a longitudinal slice of 

 the fossil be cut in the direction of these lines, and reduced to merely 

 a single cell in thickness, it will become evident that the lines in ques- 

 tion have their origin in the peculiar form and arrangement of the 

 cells of the parenchymatous tissue as above described. A somewhat 

 similar appearance may be noticed in some specimens of Halonia and 

 also in the Sigillarice ; indeed the more these fossils of the Coal- 

 measures are compared together, the greater is the affinity met with 

 in their structure. The author mentioned that, on lately examining 

 a specimen of Sigillaria reniformis, the tissues appear so much to 

 resemble those of the Calamite, as to prove the close connection of 

 these two genera ; — in fact all those fossils of this family with the 

 broad outer zones of woody tissue, such as Calamitea striata of Cotta, 

 will in all probability prove to be some species of small-ribbed Sigil- 

 laria. One other important point Mr. Dawes is enabled to prove, 

 viz. that concentric rings not only do occur in these fossils, but that 

 they are as clearly denned as in any recent dicotyledon §. 



The interior of the Calamite appears, so far as can be ascertained, 



* These small cellular spaces, being frequently roundish and pretty regular in 

 size, were considered by Unger to represent aerial canals. See Unger's Memoir 

 read at Erlingen and published by the Botanical Society of Ratisbon, Nos. 41, 42. 



f Unger has described the lighter-coloured structure as pseudo-vascular, and 

 the darker rays as the cellular tissue ; which however is not correct. 



% These linear appearances were described in the author's former paper as in- 

 dicating medullary rays ; and so also were they regarded by Unger ; but of this 

 circumstance Mr. Dawes was not previously aware. 



§ The existence of these concentric zones of periodical growth has not been 

 shown by any other observer ; indeed Unger especially alludes to their absence, 

 as a proof of the affinities of this plant with the Equisetum. 



