18& PROCEEDINGS OF THE GEOLOGICAL SOCIETY. [Jan. 21, 



stem of Sigillaria pachyderma, as figured in the ' Fossil Flora,' t. 54- ; 

 and thus appears to suggest the same explanation of the nature of 

 that anomalous dome as is here proposed. It may be observed, that 

 in the figure last quoted the stem of S. pachyderma is represented as 

 divided into several portions by apparent joints, the lowermost of 

 which, occurring just above the roots, leaves the portion below it in 

 a form very well adapted to the hypothesis in question ; but I am 

 not aware that anything similar has been noticed by others in any 

 species of Sigillaria ; and perhaps the appearance of articulations in 

 that instance may be occasioned merely by the mineral structure of 

 the stone of which the cast was composed. 



The " transverse prominences," noticed by Mr. Dawson as pro- 

 ceeding from the " core" or excentric axis of the upright stem, are 

 doubtless of the same nature with those which are often conspicuous 

 on the surface of the vascular axis of Stigmaria, and which are 

 represented in tab. 35 of the ' Fossil Flora.' They are the broken 

 remains of vascular bundles which passed from the axis to the leaves 

 or rootlets. A similar excentric vascular axis, with bundles of ves- 

 sels proceeding from it to the bases of the leaves, is described by 

 M. Ad. Brongniart in the only Sigillaria of which the internal 

 structure has yet been ascertained ; but, while the existence of the 

 solid axis may very often be distinctly traced even in the stony casts 

 of Stigmariee, it does not appear to be so distinct in the Sigillariae. 



Before quitting the subject of these remarkable extinct forms of 

 vegetable life, I may further observe, that the similarity of their vas- 

 cular tissue to that of Ferns is not a sufficient proof of any real affi- 

 nity to that tribe of plants, since Mr. Brown has ascertained that 

 vessels of a similar structure (" vasa scalariformia") constitute the 

 whole of the woody tissue of Myzodendron*, a genus of parasitical 

 flowering plants allied to the Misletoe, and totally dissimilar to Ferns. 



Mr. Dawson's explanation of the nature of the so-called Stern- 

 bergia appears by far the most probable that has yet been proposed. 

 The smooth outer coat observed by that gentleman (and of which 

 1 perceive traces in some English specimens) seems to afford an 

 almost conclusive argument against M. Brongniart's opinion, that 

 the transverse lines on the surface of the casts were the scars of 

 fallen leaves. M. Brongniart appears to have been unaware of the 

 existence of this smooth carbonized integument ; it is slightly no- 

 ticed by the authors of the * Fossil Flora,' who however seem to re- 

 gard it as adventitious, not belonging to the plant; but this, ac- 

 cording to Mr. Dawson's observations, is by no means the case. 



If a generic name be required for these bodies, that of Artisia 

 ought certainly to be adopted in preference to Sternbergia, as the 

 latter belongs to a genus of recent plants very different from these 

 fossils. 



In addition to the specimens described in Mr. Dawson's paper, 

 that gentleman has sent a fragment of a somewhat anomalous ap- 

 pearance, of which he thus speaks in a letter to me : — 



* Linnean Transactions, vol. xix. p. 231, note. 



