The gonidia of the immediately underlying zone are sparsely arranged and a few of them are found in the lower half of the cone; the hyphae of the medulla can be traced up to the apex. Zukal[442] claims to have found breathing-pores in _Cornicularia_ (_Parmelia_) _tristis_ and in several other _Parmeliae_, notably in _Parmelia stygia_. The thallus of the latter species has minute holes or openings in the upper cortex, but they are without any definite form and may be only fortuitous. [Illustration: Fig. 75 A. _Ramalina fraxinea_ Ach. A, surface view of frond. _a_, air-pores; _b_, young apothecia. × 12. B, transverse section of part of frond. _a_, breathing-pore; _f_, strengthening fibres. × 37 (after Brandt).] [Illustration: Fig. 75 B. _Ramalina strepsilis_ Zahlbr. Transverse section of part of frond showing distribution of: _a_, air-pores, and _f_, strengthening fibres. × 37 (after Brandt).] Zukal[442] published drawings of channels of looser tissue between the exterior and the pith in _Oropogon Loxensis_ and in _Usnea barbata_. He considered them to be of definite service in aeration. The fronds of _Ramalina dilacerata_ by stretching develop a series of elongate holes. Reinke[443] found openings in _Ramalina Eckloni_ which pierced to the centre of the thallus, and Darbishire[444] has figured a break in the frond of another species, _R. fraxinea_ (Fig. 75 A), which he has designated as a breathing-pore. Finally Brandt[445], in his careful study of the anatomy of _Ramalinae_, has described as breathing-pores certain open areas usually of ellipsoid form in the compact cortex of several species: in _R. strepsilis_ (Fig. 75 B) and _R. Landroensis_, and in the British species, _R. siliquosa_ and _R. fraxinea_. These openings are however mostly rare and difficult to find or to distinguish from holes that may be due to any accident in the life of the lichen. It is noteworthy that Rosendahl found no further examples of breathing-pores in the brown _Parmeliae_ that he examined in such detail. No other organs specially adapted for aeration of the thallus have been discovered. _b._ OTHER OPENINGS IN THE THALLUS. _Lobaria_ is the only genus of Stictaceae in which neither cyphellae nor pseudocyphellae are formed; but in two species, _L. scrobiculata_ and _L. pulmonaria_, the lower surface is marked with oblong or angular bare convex patches, much larger than cyphellae. They are exposed portions of the medulla, which at these spots has been denuded of the covering cortex. Corresponding with these bare spots there is a pitting of the upper surface.