Among the _Cladoniae_ the reticulate condition recurs now and again. In our native _Cladonia cariosa_ the splitting of the podetial wall is a constant character of the species, the carious condition being caused by unequal growth which tears apart the longitudinal fibres that surround the central hollow. A more advanced type of reticulation arises in the group of the _Clathrinae_ in which there is no inner chondroid cylinder. In _Cladonia aggregata_, in which the perforations are somewhat irregular, two types of podetia have been described by Lindsay[402] from Falkland Island specimens: those bearing apothecia are short and broad, fastigiately branched upwards and with reticulate perforations, while podetia bearing spermogonia are slender, elongate and branched, with fewer reticulations. An imperfect network is also characteristic of _Cl. Sullivani_, a Brazilian species. But the most marvellous and regular form of reticulation occurs in _Cl. retepora_, an Australian lichen (Fig. 71): towards the tips of the podetia the ellipsoid meshes are small, but they gradually become larger towards the base. In this species the outer tissue, though of parallel hyphae, is closely interwoven and forms a continuous growth at the edges of the perforations, giving an unbroken smooth surface and checking any irregular tearing. The enlargement of the walls is solely due to intercalary growth. The origin of the reticulate structure in the _Clathrinae_ is unknown, though it is doubtless associated with wide podetia and rendered possible by the absence of an internal chondroid layer. The reticulate structure is marvellously adapted for the absorption of water: _Cl. retepora_, more especially, imbibes and holds moisture like a sponge. [Illustration: Fig. 71. _Cladonia retepora_ Fr. From Tasmania.] F. ROOTING STRUCTURES OF CLADONIAE The squamules of the primary thallus are attached, as are most squamules, to the supporting substance by strands of hyphae which may be combined into simple or branching rhizinae and penetrate the soil or the wood on which the lichen grows. There is frequently but one of these rooting structures and it branches repeatedly until the ultimate branchlets end in delicate mycelium. Generally they are grey or brown and are not easily traced, but when they are orange-coloured, as according to Wainio[403] they frequently are in _Cladonia miniata_ and _Cl. digitata_, they are more readily observed, especially if the habitat be a mossy one.