Grand’Eury[477] has described an example of an old stem of a ribless species of _Sigillaria_, _Syringodendron bioculatum_, bearing single and double parichnos areas of nearly circular form and with a diameter of 1–2 cm. In a specimen figured by Renault and Roche[478] (_Syringodendron esnostense_) from the Culm strata in France, the parichnos scars reach a length of 3 cm. As seen in the fragment of a ribbed _Sigillaria_ represented in fig. 198, the large parichnos areas exhibit a distinct surface pitting in contrast to the fine longitudinal striation of the rib; the difference in surface-appearance is due to the nature of the tissue, which in the parichnos consists of fairly large parenchymatous elements with groups of secretory cells[479], and in the exposed cortex of elongated elements. The vertical line in the middle of fig. 198, which occurs in the middle of the rib, has probably been formed by splitting of the bark. [Illustration: FIG. 198. _Sigillaria_ with large parichnos areas. (⅓ nat. size.) M.S.] Grand’Eury’s description of fossil forests of Sigillariae in the rocks of the St Étienne[480] district affords a striking picture of these arborescent Pteridophytes; he speaks of the stems of some of the trees as swollen like a bottle at the base, characterised by the Syringodendron features and terminating below in short repeatedly forked roots of the type known as _Stigmariopsis_. Other specimens of _Sigillaria_ stumps show a marked decrease in girth towards the base; this tapered form is regarded by Grand’Eury as the result of the development of aerial columnar stems from underground rhizomes. The nature of the root-like organs of _Sigillaria_ is dealt with in the sequel: a brief reference may, however, be made to the occurrence of stumps of vertical trunks which pass downwards into regularly forked and spreading arms. These arms lie almost horizontally in the sand or mud like the underground rhizomes of _Phragmites_ and other recent plants growing in swampy situations where water is abundant and where deeper penetration of the soil would expose them to an insufficient supply of oxygen[481]. It is certain that _Sigillaria_ had no tap-root, but was supported on spreading subterranean organs bearing spirally disposed long and slender rootlets which absorbed water from a swampy soil. [Illustration: FIG. 199. Partially decorticated stem of _Sigillaria_ showing two zones of cone-scars. From a cast in the Sedgwick Museum, Cambridge. M.S. (⅕ nat. size.)]