DAWSON — 8IGILLABIA, CALAMIXES, AND CALAMODENDRON. 157 



"^Oalamites, but of Cahmodemlron, rests on different grounds, and is 

 -(iopported by the fact that some of the larger stems which may bo 

 ^^pposed to represent the external surface of Calamodendron, have 

 tomid nodes similar to those of the branches of Asterophitllites. 

 i|N»m8 of this kind are sometimes found in an erect position in the 

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

 4tf ordinaiy Calamites. 



' 6. The microscopic stnicture oi 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 lacunse, or air-ceUs, like those of modern Equiseta ; 

 and the tissue intervening between these contains largo vasiform 

 tabes marked on the surface with numerous rows of small pores 

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

 OMJ.), ai, 1 which bear some resemblance to the fibres of Dicty- 

 ■oecylon as described by Williamson (PI. IX. fig. lU). This struc- 

 'tnre has been illustrated by Goeppert, linger, Schimper, and others ; 

 snd I have verified it by the microscopic examination of numerous 

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

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

 .€oal.' 



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

 cavities of stems having a thick Avoody envelope disposed in wedges 

 ileparated by intervening tracts of cellular tissue, which, according 

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

 tmaller medullary rays occur in the intervening wedges, and pre- 

 senting the same discigerous and pseudo-scalariform tissues ob- 

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

 'Calamodendron with the tissues found attached to them. These 

 stems, no doubt, have lacuna? like those of Calamites, and resemble 

 'tiiem in general arrangement of parts, but differ in the much greater 

 developm.ent of the woodj'^ 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 

 l)elong to these plants. There has, however, been some confusion 

 between the fruit of Calamites and Asterophyllitis, A\hich demands 

 attention from those who have access to the specimens. 



It results from the facts above stated that the true equisetaeeous 

 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 tlieir 

 affinities. Whethf, as Schimpcr supposes, they were merely an- 

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

 the equable climate of the Coal-pjriod 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 ^y increasing depr sits of sediment, seems to 



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