248 PEOCEEDINQS OF THE GEOLOGICAL SOCIETY. [Maich 24, 



2. On the Stetjctuee and Apfinities of Sigillaria and allied 

 Geis^eea. By W. Caeetjthees. 



[Plate X.] 



The genus Sigillaria is one of the most abundant and important 

 among- the plants of the Carboniferous period. But, except that it 

 was a large tree with a fluted and scarred stem, and had immense 

 succulent roots, little is certainly known regarding it. The struc- 

 ture of the root is well known, having frequently formed the sub- 

 ject of investigation. Numerous specimens of stems have been pub- 

 lished, as examples of the genus ; but with the exception of that 

 described by Brongniart under the name of Sigillaria elegans, they 

 belong rather to the genus Lepidodendron ; and even S. elegans does 

 not represent the most characteristic form of the genus. The stem 

 was most probably simple, though in some species it was certainly 

 branched. The foliage in some forms was composed of long linear 

 leaves ; and Goldenberg has figured organs of reproduction in the 

 form of small round sporangia, several of which were borne on the 

 somewhat dilated bases of the leaves at the termination of a branch. 



The affinities of the genus have chiefly been deduced from the 

 structure of the stem and roots ; and in accordance with the views 

 taken by the different interpreters has been the place they have 

 given it. Some, like Corda and Martins, have held it to be a poly- 

 petalous dicotyledon, while, on the other hand, Dr. Hooker, with a 

 little hesitancy, places it among Lycopodiacece beside Lepidodrendron. 

 The generally received opinion is somewhat intermediate, that it is 

 a gymnosperm belonging to an extinct type. Brongniart first enun- 

 ciated this view ; and it has been subsequently maintained by Gop- 

 pert, linger, &c., and recently by Dawson in an important and 

 elaborate paper on the Coal Formation of Nova Scotia, published 

 in the Journal of this Society in 1866, and two years later in his 

 ' Acadian Geology.' 



I propose to investigate shortly the grounds upon which these emi- 

 nent palaeontologists have given this position to the genus, and how 

 far their interpretations agree with the actual structure of the plant. 



I shall first consider the structure of the root, the relation of which 

 to the stem has been established beyond question. The investiga- 

 tions of Mr. Binney on the external form and of Prof. King and Dr. 

 Hooker on the internal structure make it unnecessary that I should 

 describe at any length the root so well known by the name of Stig- 

 maria. The general structure may be given in a few words. It was 

 a thick root having a medulla of considerable size, surrounded by a 

 cylinder of scalariform vessels ; and this again was invested by a large 

 mass of cortical parenchyma. From numerous pits on the outer sur- 

 face of this cortical layer proceeded the long cellular rootlets, each 

 furnished with a small bundle of firm scalariform vessels that had its 

 origin in the vascular cylinder. In the arrangement of the parts, 

 and in the general aspect of a transverse section of the stem, it 

 agrees with the structure of the stems of Cycadece-, and of the 

 fleshy Eupliorhiaceoi and Cactece. It is unnecessary to say that 



