374 On l^igillaria, Stigmaria^ and Neuropteris, 



face of the central portion" of a ^tigmana ; on the contrary, it is shewn 

 to be, at least the crown, merely the impression of the under surface of 

 the fossil, in shorty that it is nothing more than a convex mass of har- 

 dened mud answering to the under side or concavity of a root. 



We will now proceed to give a brief view of the principal evidences 

 which have led to the opinion that StigmaHa is a root, and that it belongs 

 to Sigillaria. 



First, the correspondency of the sinuous lines on the crown of the 

 above dome-shaped specimen, with those observable on the under side of 

 the root-stock of a Sigillaria in the Newcastle Museum ; second, the 

 correspondency of two furroivs placed at right angles to each other, 

 observable on the under side or concavity of the root stock on two speci- 

 mens of ^igillaria, with the ridges seen on the crown or convexity of the 

 dome-shaped specimen ; third, the root-like form of perfect speci- 

 mens of Stigmaria ; fourth, the position of the external appendages 

 of the last specimens, which is such, that they must have penetrated the 

 now consolidated mud in which they are imbedded, as shewn by Stein- 

 hauer and Button : fifth, the resemblance of the furrows on the origins of 

 the branches of Stigmaria with those on the base of Sigillaria, thereby 

 shewing the one to be a continuation of the other ; sixth, the similarity 

 between the internal structure of SigiUaria and Stigmaria.'^ 



Some points connected with the internal structure of Stigmaria are 

 alluded to, and it is shewn that the large intercellular spaces which cha- 

 racterize the ligneous cylinder of this plant, are not true ^' great medul- 

 lary rays," as has been generally supposed, but openings which served 

 for the passing out of the cords from the vascular system into the ex- 

 ternal appendages, and analogous to what is observable in Anahathra 

 and Lepidodendron^ Some additional information as to the internal struc- 

 ture of these latter fossils is given as derived from the examination of a 

 number of sections. 



Certain objections which have been urged against Stigmaria being a 

 root, are next considered, — especially the spiral arrangement of the 

 appendages, and the presence of a pith ; but the force of these objec- 

 tions, it is contended, is considerably diminished if we look upon this 

 fossil as combining the form of a true JRadix with the characters of a 

 llhizoma^ — at least in such of the latter as exhibit, in the regular arrange- 

 ment of their fibrils, and in their anatomy, but little difference from what 

 obtains in the stem. 



Respecting the situation of SigiUaria in the vegetable kingdom, al- 

 though its cycadeous character is fully admitted with Brongniart, the 

 probability of its being related to the Angiospermous Dicotyledons as 

 supposed by this learned botanist, is shewn to be somewhat remote : 



* From this similarity, M. Brongniart was led to suppose that Stigmaria 

 would turn out to be the root of Sigillaria, 



