of the Fossil Plants of the genus Sigillaria. 11 



not in others. A similar arrangement is to be seen in some Tree Ferns, 

 especially in a New Zealand species of Cyathea, in which are observable 

 some small vascular bundles disposed irregularly throughout the centre 

 or pith, in addition to the larger ones constituting the nearly regular 

 but broken circle, so characteristic of the stems of the Vascular Cryp- 

 togams. 



Besides Stigmaria and Anahathra, there are other two remarkable fos- 

 sils, which Brongniart compares with Sigillaria elegans, namely, Lepido- 

 dendron and Frotoptcris Cotteana, Corda {Lepidodendron punctatum, 

 Sternb,). A transverse section of the stem of the first, shews that it is 

 chiefly composed of cellular tissue, in which is imbedded an excentrical- 

 ly situated and continuous circle, composed of vessels, or tubular cells, 

 transversely barred on all their walb. This circle exhibits no traces of 

 medullary rays, nor are the vessels composing it arranged in radiating 

 series. It would therefore appear, that the circle constituted the vas- 

 cular system, and as such it may be considered analogous to the medul- 

 lary sheath of Sigillaria elegans. 



Protopteris Cotteana^ which was formerly included by Brongniart in his 

 first section of the genus Sigillaria, is undoubtedly a Tree Fern, and ap- 

 pears, from certain peculiarities of its small bundles of vessels dispersed 

 throughout the central cellular tissue, and of the large bundles situated 

 externally to the last, and forming a narrow sinuous cylinder, to have 

 been a representative, in the carboniferous epoch, of the existing genus 

 Dicksonia. 



Having adverted to Tree Ferns, and as Brongniart formerly maintain- 

 ed that Sigillaria was related to this family, the question naturally arises 

 as to how far these two forms resemble or difler from each other. In 

 answer, Brongniart himself says, I admit at once that the external struc- 

 ture of the latter, as far as Sigillaria elegans has been made known to us, 

 is essentially different from that of Ferns, and the allied families, by 

 Bome very important characters ; the nature of the ligneous or vascular 

 tissue certainly establishes some analogy between them ; but its arrange- 

 ment is altogether different. In short, the arrangement of the tissue in 

 radiating series, is a character foreign to all Cryptogams ; it is, on the 

 contrary, characteristic of the Dicotyledons ; but it belongs, with nume- 

 rous modifications, to the whole of this immense division of the vegetable 

 kingdom from the Gymnosperms, the organization of which is compara- 

 tively simple, to those families whose structure is more complicated. It 

 therefore appears impossible to doubt that Sigillaria belongs to the class 

 of Dicotyledonous plants. But is it to the group of Gymnosperms, so 

 abundant in a fossil state, and characteristic of the carboniferous strata, 

 or to the Angiospcrmous division, which, as far as is known, appears to 

 be absent from those ancient formations ? The uniformity of the tissue, 

 and the absence of true spiral vessels in the ligneous cylinder, are cha- 

 racters proper to the Gymnosperms, but are rarely found amongst the 

 true Angiospermous Dicotyledons. All the probabilities, then, are in fa- 

 vour of this fossil being a Gymnosperm. It would be difficult, however, to 



