SIGILLARIA AND STIGMARIA. 



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des quatre racines priraaires. Cette suture n'est autre chose qu'une ligne de contact 

 produite par Pepaississement de ces quatre racines (voy. notre pi, fig. 14) ; elle se 

 continue aussi vers le haut entre ces memes racines." 



V. Concluding Remarks. 



When Brongniart described his Sigillaria elegans, the Rev. Mr. Harcourt's Lepido- 

 dendron, Lindley and Button's Stlgmaria, and Mr. Witham's Anabathra, he had before 

 him all the materials then known, for examining the structure of those plants, that the 

 Coal-measures had afforded. Subsequently Corda added the Biploxylon cycadoideum. 

 Then Goeppert described his Stigmaria with the vascular bundles in the pith. But in 

 all these specimens, except the last, the structure of the piths was more or less wanting. 

 The first time that anything was published as to stems with vascular tubes in their piths 

 was in my paper in the ' Quarterly Journal of the Geological Society,' and this was 

 further extended in my Memoir in the ' Philosophical Transactions,' where were described 

 larger specimens of Sigillaria vascularis and Dijjloxglon cycadoideum, all showing 

 structure similar to that of the smaller ones first described, with the exception of the 

 Biploxylon having the edges of the woody bundles of the inner radiating cylinder slightly 

 lunette-shaped, and running into the pith, like those described by Corda in his 

 specimen, but in a less degree. Professor King, in his description of Witham's 

 Anabathra, shows it to be like Sigillaria vascularis, except in the pith, which was not 

 distinctly shown. Each plant had the same medulla, inner radiating cylinder traversed 

 by large and small medullary rays, since termed primary and secondary, the same zone of 

 lax parenchymatous tissue, gradually passing into prosenchyma, and traversed by 

 vascular bundles leading to the leaves, and which, although traced to the outside of the 

 inner radiating cylinder, could not be absolutely proved to be connected Avith the large 

 medullary rays, and the same outer bai-k generally converted into bright coal. It was 

 also asserted that the small Lepidodendroid stem gradually passed into the irregularly 

 ribbed and furrowed Sigillaria, and that the open-wedged Stigmaria belonged to 

 Diploxylo7i cycadoideum, as its root, Avhilst the close-wedged one belonged to Sigillaria 

 vascularis. Since these, in this Monograph, Mr. Dawes' specimen of Lepidodendron 

 Harcourtii has been described, and shown to contain a medulla of orthosenchymatous 

 tissue, which Mr. Harcourt's specimen did not afford. The question now for con- 

 sideration is this, — is the latter to be regarded as the type of the structure of Lepido- 

 dendron, or is the new plant described by me to be so regarded, taking the evidence of 

 internal structure, without regarding the external character. So far as the former goes, 

 it appears to me desirable for the present to limit the genus Lepidodendron to the old 

 type; and therefore I object to Mr. Carruthers taking my small specimens as Lepi- 

 dodendron, and Professor Wihiamson taking my large ones as Biploxylon vasculare. My 



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