OF THE WOODY ZONE IN CALAMITE. 167 



proceed directly outwards towards the bark. It is one of 

 these groups, transversely divided, which produces the ap- 

 pearance of a transversely divided branch, seen in fig. 15- 

 In the centre of the latter group the cells and vessels are 

 divided at right angles to their longer axes, whilst the 

 peripheral ones run in the plane of the section. I think 

 there can be no doubt that this arrangement was destined 

 to supply some external appendages of the main stem with 

 vascular tissue. Whether these appendages were branches 

 or leaves is doubtful ; but I incline to the former opinion. 



Mr. Binney has recorded somewhat analogous arrange- 

 ments in his Tab. 3. fig. 4. 



Before attempting to interpret the facts which I have 

 described, a further glance at the discoveries of some 

 other recent observers is necessary. 



Nothing could be more unsatisfactory than the state of 

 our knowledge of the internal structure of the stems of 

 Calamites prior to the investigations of M. Unger ; and 

 valuable as those were, they only threw light upon one 

 branch of the question. Guided by that light, M. Adolphe 

 Brongniart suggested, in his ' Tableau des genres de Ve- 

 getaux Fossiles'*, that two distinct groups of plants had 

 hitherto been confounded under the name of Calamites. 

 He proposed that these should henceforth be separated, 

 retaining the old name for one section, which he regarded 

 as allied to the Equisetce, and employing the generic term 

 Calamodendron for the other, which he thought ought to be 

 ranged amongst the Gymnospermous Dicotyledons. The 

 structure of the genus Calamitea of Cotta, as demonstrated 

 by Unger, is regarded by M. Brongniart as typical of his 

 Calamodendron. He describes this genus as exhibiting, 

 amongst other features, a woody cylinder composed of 

 large radiating vertical tracts of transversely barred vessels 

 intermingled with true medullary rays, alternating with 

 * Dictionnaire Universelle d'Histoire Naturelle. 



