In _Variolaria_, a genus closely allied to or generally included in _Pertusaria_, Darbishire[598] has described the primordial tissue as taking rise almost at the base of the crustaceous thallus: strands of delicate hyphae, staining blue with iodine, mount upwards from that region through the medulla and gonidial zone[599]. The ascogonium does not appear till the surface is almost reached. _cc._ _GRAPHIDEAE._ Several members of the Graphidaceae were studied by G. Wolff[600]: she demonstrated the presence of carpogonia with emerging trichogynes in _Graphis elegans_, a species which is distinguished by the deeply furrowed margins of the lirellae (Fig. 89). Before the carpogonia appeared it was possible to distinguish the cushion-like primordial tissue of the apothecium in the thallus which is almost wholly immersed in the periderm layers of the bark on which it grows. The trichogynes were very sparingly septate, and a rather large nucleus occupied a position near the tip of the terminal cell. The dark carbonaceous outer wall makes its appearance in this species at an early stage of development along the sides of the lirellae, but never below, as there is always a layer of living cells at the base. After the first-formed hymenium is exhausted, these basal cells develop a new apothecium with a new carbonaceous wall that pushes back the first-formed, leaving a cleft between the old and the new. This regenerating process, somewhat analogous to the formation of new apothecia in _Pertusaria_, may be repeated in _Graphis elegans_ as many as five times, the traces of the older discs being clearly seen in the channelled margins of the lirellae. [Illustration: Fig. 98. _Cladonia decorticata_ Spreng. Vertical section of squamule and primordium of podetium. _a_, developing podetium; _b_, probably fertile hyphae; _c_, cortical tissue; _d_, gonidial cells. 1 × 600 (after Krabbe).]