[Illustration: Fig. 575. A stone on which various Lichens are growing, such as (passing from left to right) a Parmelia, a Sticta, and on the right, Lecidia geographica, so called from its patches resembling the outline of islands or continents as depicted upon maps. 576. Piece of thallus of Parmelia conspersa, with section through an apothecium. 577. Section of a smaller apothecium, enlarged. 578. Two asci of same, and contained spores, and accompanying filaments; more magnified. 579. Piece of thallus of a Sticta, with section, showing the immersed apothecia; the small openings of these dot the surface. 580. Cladonia coccinea; the fructification is in the scarlet knobs, which surround the cups.] 516. =Fungi.= For this immense and greatly diversified class, it must here suffice to indicate the parts of a Mushroom, a Sphæria, and of one or two common Moulds. The true vegetation of common Fungi consists of slender cells which form what is called a _Mycelium_. These filamentous cells lengthen and branch, growing by the absorption through their whole surface of the decaying, or organizable, or living matter which they feed upon. In a Mushroom (Agaricus), a knobby mass is at length formed, which develops into a stout stalk (_Stipe_), bearing the cap (_Pileus_): the under side of the cap is covered by the _Hymenium_, in this genus consisting of radiating plates, the gills or _Lamellæ_; and these bear the powdery spores in immense numbers. Under the microscope, the gills are found to be studded with projecting cells, each of which, at the top, produces four stalked spores. These form the powder which collects on a sheet of paper upon which a mature Mushroom is allowed to rest for a day or two. (Fig. 581-586.) 517. The esculent Morel, also Sphæria (Fig. 585, 586), and many other Fungi bear their spores in sacs (asci) exactly in the manner of Lichens (515). [Illustration: Fig. 581. Agaricus campestris, the common edible Mushroom. 582. Section of cap and stalk. 583. Minute portion of a section of a gill, showing some spore-bearing cells, much magnified. 584. One of these, with its four spores, more magnified.] [Illustration: Fig. 585. Sphæria rosella. 586. Two of the asci and contained double spores, quite like those of a Lichen; much magnified.]