_a._ Thallus homoiomerous, but not gelatinous, branching according to the mode of growth of the Algæ: _Cœnogonium_. _b._ Thallus homoiomerous, gelatinous: _Collema_ (Fig. 132), with Algæ of the genus _Nostoc_; _Leptogium_. _c._ Thallus heteromerous, crustaceous: _Pertusaria_ (Fig. 140), _Lecidea_, with apothecia open from the beginning; _Lecanora_, with apothecia, which in the beginning are closed, later on open, but with a rim formed by the thallus (Fig. 138); _Bæomyces_, whose apothecia are borne on a stem formed by the thallus. _d._ Thallus heteromerous, foliaceous: _Parmelia_ (_P. saxatilis_; _P. parietina_, Wall-Lichen, Fig. 141, is yellow, very frequent on tree-stems, stone-walls, tiles); _Physcia_ (_P. ciliaris_, frequent on tree-stems); _Sticta_ (_S. pulmonacea_, Lung-Lichen, on tree-stems); _Peltigera_, especially on the Moss among trees; _Umbilicaria_, on rocks. _e._ Thallus heteromerous, fruticose: _Cetraria_ (_C. islandica_), “Iceland Moss,” with an olive-brown, flat, furrowed, fringed thallus, on heaths; _C. nivalis_, white, in the Polar regions; _Evernia_, _Ramalina_, _Usnea_ (_U. barbata_, Beard-Lichen, Fig. 143); _Roccella_, _Stereocaulon_, _Cladonia_, of which the genus _C. rangiferina_, Reindeer-Moss (Fig. 142) is important; _Cladonia_ has two kinds of thallus, one scaly and leaf-like, the other erect, which bears the apothecia and may be fruticose (Fig. 142), or cupular (Fig. 144); they grow in soil in forests and on heaths. [Illustration: FIG. 142.--_Cladonia rangiferina_: _s_ ascocarp.] [Illustration: FIG. 143.--_Usnea barbata_: _s_ ascocarp. (Slightly magnified.)] [Illustration: FIG. 144.--_Cladonia pyxidata._] Sub-Class 2. =Basidiomycetes.= This sub-class embraces the most highly developed Fungi, with large “fruit-bodies,” which in ordinary language we shortly term Funguses, Toadstools, or Mushrooms. They have no sporangia, but reproduce only by means of basidiospores, conidia, chlamydospores and oidia. The chief characteristic of this sub-class is the _basidium_ (Fig. 145), _i.e._ the conidiophore, which has a distinctive form, and bears a definite number (generally 4) of characteristically shaped conidia (basidiospores, Fig. 145 _c_, _d_, _e_). [Illustration: FIG. 145.--Development of spores in _Corticium_.]