Our knowledge of Sigillarian cones is too incomplete to admit of a detailed comparison with the strobili of _Lepidodendron_ or with those of recent Pteridophytes. There can, however, be little doubt that Goldenberg[514] was correct in his selection of _Isoetes_ as the most nearly allied recent plant so far as the fertile leaves are concerned. It would seem that the sporangia were comparatively delicate structures which have left no clearly defined remains of their walls in the carbonised specimens; Kidston, indeed, speaks of the hollow bases of the sporophylls as holding the spores, but this is hardly likely to have been the case. Our knowledge of the anatomy of _Sigillariostrobus_ is practically nil, but in one specimen of a _Sigillaria elegans_ stem Kidston[515] describes the structure of the tissues as seen in a transverse section of a scar of a fertile shoot; from this we learn that the stele was composed exclusively of primary tracheids forming a solid strand without a pith. It is probable that the cones of _Sigillaria_ were heterosporous, but in no instance have undoubted microspores been discovered; the megaspores in each megasporangium were fairly numerous as in _Isoetes_ (fig. 133, E). In one species, _Sigillariostrobus major_ (Germar), from Permian rocks of France and Germany, Zeiller[516] states that the whole of a single cone bore megaspores (0·8–1 mm. in diameter) only; this is, however, not opposed to the idea of heterospory, as we find instances in _Selaginella_ of strobili bearing one kind of spore only (cf. p. 56). In a few instances, it has been possible to correlate cones with certain species of _Sigillaria_, but in most cases the strobili occur as isolated fossils. iv. _The structure of Sigillarian stems._