OF THE WOODY ZONE IN CALAMITE. 159 



projecting ridges (c) ; these, whicli lose tliemselves in the 

 nodes, are separated from each other by more depressed 

 excavated grooves {d) corresponding with the elevated longi- 

 tudinal ridges of the common Calamites. A slight micro- 

 scopic examination, demonstrates that these two features 

 (c and d) owe their existence to two very different elemen- 

 tary tissues, arranged in vertical laminae, or wedges, which 

 radiate in alternating series from the medulla to the peri- 

 phery of the woody zone. It will be remembered that in 

 1 84 1, linger, in a work of Petzholdt's (' Ueber Kalamiten- 

 und Steinkohlen-Bildung,'' Dresd. u. Leipz. 1841, Tabs. 

 7 and 8), called attention to a similar arrangement of 

 tissues in the Calamitea striata of Cotta, in which one of 

 the alternating structures consisted of transversely barred 

 fibres, such as are seen in ^tigmaria, traversed by medullary 

 rays, and of intermediate tissues composed of smaller and 

 more numerous woody fibres, each radiating series of 

 which had one large central medullary ray. The general 

 type just described resembles, in its broad outlines, what 

 I find in my specimen; but in their minute details the 

 two plants are different. 



As already mentioned, the raised ridges and the inter- 

 mediate depressions in fig. 2 consist of two very distinct 

 structures, each of the former (c) being composed of numer- 

 ous longitudinally disposed vessels of a reticulated type, 

 whilst the latter consist of oblong prosenchymatous cells. 

 In the transverse section, both these structures are seen 

 arranged in the same manner, radiating in equally regular 

 parallel lines from centre to circumference. I shall hence- 

 forth speak of these alternating structui'es as composing 

 the vascular and the prosenchymatous tracts. 



Fig. 3 represents a portion of a transverse section made 

 in the centre of an internode, as at 2 a, the figure being 

 almost limited to two of the vascular tracts and an inter- 

 vening prosenchymatous one. As the crenulated outline 



