The crustaceous thallus is more or less firmly adherent to, or confused with, the substratum. Further advance to a new type of thallus is made when certain hyphal cells of soredium or granule take the lead in an ascending direction both upwards and outwards. As growth becomes definitely apical or one-sided, the structure rises free from the substratum, and small lobules or leaflet-like squamules are formed. Each squamule in this type of thallus is distinct in origin and not merely the branch of a larger whole. In a few lichens the advance from the crustaceous to the squamulose structure is very slight. The granules seem but to have been flattened out at one side, and raised into minute rounded projections such as those that compose the thallus of _Lecanora badia_ generally described as “subsquamulose.” The squamulose formation is more pronounced in _Lecidea ostreata_, and in some species of _Pannaria_; and the whole thallus may finally consist of small separate lobes as in _Lecidea lurida_, _Lecanora crassa_, _L. saxicola_, species of _Dermatocarpon_ and the primary thallus of the _Cladoniae_. Most of these squamules are of a firm texture and more or less round in outline; in some species of _Cladonia_, etc., they are variously crenate, or cut into pinnate-like leaflets. Squamulose lichens grow mostly on rocks or soil, occasionally on dead wood, and are generally attached by single rhizoidal hyphae, either produced at all points of the under surface, or from the base only, growth in the latter case being one-sided. In a few instances, as in _Heppia Guepini_, there is a central hold-fast. A frequent type of squamulose thallus is that termed “placodioid,” or “effigurate,” in which the squamulose character is chiefly apparent at the circumference. The thallus is more or less orbicular in outline; the centre may be squamulose or granular and cracked into areolae; the outer edge is composed of radiating lobules closely appressed to the substratum (Fig. 42). [Illustration: Fig. 42. _Placodium murorum_ DC. Part of placodioid thallus with apothecia × 2.] All lichens with this type of thallus were at one time included in the genus _Placodium_, now restricted by some lichenologists to squamulose or crustaceous species with polarilocular spores. Many of them rival _Xanthoria parietina_ in their brilliant yellow colouring. [Illustration: Fig. 43. _Lecania candicans_ A. Zahlbr., with placodioid thallus, reduced (S. H., _Photo._).] There are also greyish-white effigurate lichens such as _Lecanora saxicola_, _Lecania candicans_ (Fig. 43) and _Buellia canescens_, well-known British species. B. TISSUES OF SQUAMULOSE THALLUS The anatomical structure of the squamules is in general somewhat similar to that of the crustaceous thallus: an upper cortex, a gonidial zone, and below that a medullary layer of loose hyphae with sometimes a lower cortex.