DAWSOX SIQILLIRIA, CAL\JIIIB3, AND CALAMODEXJJKO:^?. 157 



Calamites, but of Calamodendron, rests on different grounds, and is 

 supported by the fact that some of the larger stems which may be 

 supposed to represent the external surface of Calamodendron, have 

 tumid nodes similar to those of the branches of Aster ophyllites. 

 Stems of this kind are sometimes found in an erect position in the 

 Coal-measures of Nova Scotia, and are manifestly distinct from those 

 of ordinary Calamites. 



5. The microscopic stnieture of Calamites is not precisely iden- 

 tical with that of Calamodendron, though the latter may be regarded 

 as a more advanced type of the former. The Calamites have a thin 

 outer coat with lacunae, or air-cells, like those of modern Equiseta ; 

 and the tissue intervening between these contains large vasiform 

 tubes marked on the surface with numerous rows of small pores 

 (" multiporous tissue " of my papers on the Structures in Coal, 

 «fec.), and which bear some resemblance to the fibres of Dicty- 

 oxylon as described by "Williamson (PL IX. fig. 19). This struc- 

 ture has been illustrated by Goeppert, linger, Schimper, and others ; 

 and I have verified it by the microscopic examination of numerous 

 flattened Calamite-stems in the shales and coarse coals. Facts of 

 this kind kind were mentioned in my paper on the ' Structures in 

 Coal.' 



The Calamodendra, on the other hand, are casts of the medullary 

 cavities of stems having a thick woody envelope disposed in wedges 

 separated by intervening tracts of cellular tissue, which, according 

 to Williamson, are of the nature of large medullary rays, while 

 smaller medullaiy rays occur in the intervening wedges, and pre- 

 senting the same discigerous and pseudo-scalariform tissues ob- 

 served in Sigillaria. I have represented in Plate IX. two forms of 

 Calamodendron with the tissues found attached to them. These 

 stems, no doubt, have lacunte like those of Calamites, and resemble 

 them in general arrangement of parts, but dift'er in the much greater 

 development of the woody tissue, and, in some species at least, in 

 the character of this tissue. 



6. The fructification of Calamites I have not found in connexion 

 with the stems. I have no doubt, however, that some of the spikes 

 of fructification described by authors as the fruit of Calamites, really 

 belong to these plants. There has, however, been some confusion 

 between the fruit of Calamites and Asterophyllites, which demands 

 attention from those who have access to the specimens. 



It results from the facts above stated that the true equisetaceous 

 Calamites are well known to us by their external forms, habit of 

 growth, and foliage, as well as by their internal structure ; and on 

 all these grounds no reasonable doubt can be entertained as to their 

 afiinities. Whether, as Schimper supposes, they were merely an- 

 nual stems like those of modern Equiseta, admits of more doubt. In 

 the equable climate of the Coal-period such stems may have con- 

 tinued growing from year to year. Nor do I think that their rhi- 

 zomata were relatively so important as those of Equiseta. In some 

 of the species, at least, the erect stem itself, fortified by adventitious 

 roots, and partly buried by increasing deposits of sediment, seems to 



