THE CARBONIFEROUS AND PERMIAN FLORAS. 461 



pit or depression in its centre. From each of these pits there 

 proceeds, in perfect examples, a long cylindrical rootlet ; but 

 in many cases these have altogether disappeared. In its in- 

 ternal structure, Stigmaria exhibits a central pith surrounded 

 by a sheath of scalariform vessels, the \Yhole enclosed in a 



Fig. 710. — Stigmaria ficoides, one fourth of the natural size. Carboniferous. 



cellular envelope. The Stigmarice are generally found rami- 

 fying in the " underclay," which forms the floor of a bed of 

 coal, and which represents the ancient soil upon which the 

 Sigillarim grew. 



Of the remaining genera of the Sigillarioids, Rhytidoleyis is 

 the most important. It is characterised by the possession of 

 large, hexagonal, tripunctate areoles, and narrow, often trans- 

 versely striate ribs. In Favidaria, lastly, the smaller branches 

 were destitute of ribs, with elliptical, spirally-disposed areoles. 

 The stem branched dichotomously — like that of a Lepidodcn- 

 dron — and the leaves were broad, with numerous parallel 

 veins, approximating to the leaves of Cordaites. 



f. ConifercB. — True Conifers have long been known to occur 

 in the Carboniferous rocks. They belong to the genera 

 Dadoxylon, Palceoxylon, Araucarioxylon, and Pinites. They 

 are recognised by the great size and concentric rings of their 

 prostrate, rarely erect trunks, and by the fact that the micro- 

 scope exhibits punctated fibres in their wood. Their fruit is 

 unknown, unless, as is very probable, it is constituted by the 

 so-called Trigonocarpa. If this be the case, the Carbonifer- 

 ous Conifers must have been " Taxoid," resembling the recent 

 Yews in producing berries instead of true cones. The so- 



