_c._ CORTICAL TISSUE. In some species a cortex of the decomposed type of thick-walled conglutinate hyphae is present, either continuous over the whole surface of the podetium, as in _Cl. gracilis_ (Fig. 68), or in interrupted areas or granules as in _Cl. pyxidata_ (Fig. 69) and others. In _Cl. degenerans_, the spaces between the corticated areolae are filled in by loose filaments without any green cells. _Cl. rangiferina_, _Cl. sylvatica_, etc. are non-corticate, being covered all over with a loose felt of intricate hyphae. [Illustration: Fig. 68. _Cladonia gracilis_ Hoffm. (S. H., _Photo._).] [Illustration: Fig. 69. _Cladonia pyxidata_ Hoffm. (S. H., _Photo._).] In the section _Clathrinae_ (_Cl. retepora_, etc.) the cortex is formed of longitudinal hyphae with thick gelatinous walls. _d._ SOREDIA. Frequently the podetium is coated in whole or in part by granules of a sorediate character—coarsely granular in _Cl. pyxidata_, finely pulverulent in _Cl. fimbriata_. Though fairly constant to type in the different species, they are subject to climatic influences, and, when there is abundant moisture, both soredia and areolae develop into squamules on the podetium. A considerable number of species have thus a more or less densely squamulose “form” or “variety.” C. DEVELOPMENT OF THE SCYPHUS Two types of podetia occur in _Cladonia_: those that end abruptly and are crowned when fertile by the apothecia or spermogonia (pycnidia), or if sterile grow indefinitely tapering gradually to a point (Fig. 70); and those that widen out into the trumpet-shaped or cup-like expansion called the scyphus (Fig. 69). Species may be constantly scyphiferous or as constantly ascyphous; in a few species, and even in individual tufts, both types of podetium may be present. [Illustration: Fig. 70. _Cladonia furcata_ Schrad. Sterile thallus (S.H., _Photo._).] Wainio[398], who has studied every stage of development in the _Cladoniae_, has described the scyphus as originating in several different ways: _a._ FROM ABORTIVE APOTHECIA. In certain species the apothecium appears at a very early stage in the development of the podetium of which it occupies the apical region. Owing to the subsequent formation of the tubular cavity in the centre of the stalk, the base of the apothecium may eventually lie directly over the hollow space and, therefore, out of touch with the growing assimilating tissues; or even before the appearance of the tube, the wide separation between the primordium of the apothecium and the gonidia, entailing deficient nutrition, may have produced a similar effect. In either case central degeneration of the apothecium sets in, and the hypothecial filaments, having begun to grow radially, continue to travel in the same direction both outwards and upwards so that gradually a cup-shaped structure is evolved—the amphithecium of the fruit without the thecium.