OF THE WOODY ZONE IN CALAMITE. 173 



a pleurenchymatous arrangement and aspect ; so that in all 

 these respects my specimen approaches nearer to the 

 Gymnospermous Exogens than to the Acrogens. In the 

 Sigillaria vascularis described by Mr. Binney (Phil. Trans- 

 actions, 1865), we find abundance of the identical form of 

 prosenchyma seen in my Calamite, associated with cellular 

 tissue, scalariform vessels, and muriform medullary rays ; 

 whilst in Sigillaria Brownii^ according to Dr. Dawson, we 

 have an inner cylinder of scalariform vessels surrounded by 

 an outer one of true glandular fibre. 



It is clear that all these plants exhibit, so far as their 

 stems are concerned, indications of mutual affinity with 

 Acrogenous Cryptogams on the one hand, and with Gymno- 

 spermous Exogens on the other. The prevalence of cellular 

 and scalariform tissues points in the former direction, 

 whilst the arrangement and apparently exogenous mode of 

 growth, both of their vascular and prosenchymatous ele- 

 ments, are suggestive of the latter. This is especially the 

 case with the Calamites, which seem to me to constitute 

 a well-defined link, connecting the Exogens with the 

 Acrogens. 



But whilst it appears reasonable to locate the Calamites, 

 as a whole, in the position just indicated, the minor dif- 

 ferences which the several types seem to present suggest 

 the necessity for some change in their generic grouping. 

 I would therefore propose that, until the correctness or 

 otherwise of Brongniart's opinion that there exists an 

 Equisetiform class of Calamites is determined, we retain 

 his two genera of Calamites and Calamodendron. The 

 genus Calamites to embrace all the Equisetaceous forms, if 

 any such really exist, whilst Calamodendron may com- 

 prehend the Calamitea of Unger, and possibly Mr. Binney^s 

 specimens, the genus being characterized by the prevalence 

 of scalariform vessels and medullary rays, and by the 

 absence of verticillate medullary radii. 



