Fig. 49.—Basidiomycetes. A, common puff-ball (Lycoperdon). B, earth star (Geaster). A, × ¼. B, one-half natural size.
If we examine microscopically the youngest specimens procurable, freeing from air with alcohol, and mounting in water or dilute glycerine, we find it to be a little, nearly globular mass of colorless filaments, with numerous cross-walls, the whole arising from similar looser filaments imbedded in the substratum ([Fig. 48], G). If the specimen is not too young, a denser central portion can be made out, and in still older ones ([Fig. 48], H) this central mass has assumed the form of a short, thick stalk, crowned by a flat cap, the whole invested by a loose mass of filaments that merge more or less gradually into the central portion. By the time the spore fruit (for this structure corresponds to the spore fruit of the Ascomycetes) reaches a height of two or three millimetres, and is plainly visible to the naked eye, the cap grows downward at the margins, so as to almost entirely conceal the stalk. A longitudinal section of such a stage shows the stalk to be composed of a small-celled, close tissue becoming looser in the cap, on whose inner surface the spore-bearing ridges (“gills” or Lamellæ) have begun to develop. Some of these run completely to the edge of the cap, others only part way. To study their structure, make cross-sections of the cap of a nearly full-grown, but unopened, specimen, and this will give numerous sections of the young gills. We find them to be flat plates, composed within of loosely interwoven filaments, whose ends stand out at right angles to the surface of the gills, forming a layer of closely-set upright cells (basidia) ([Fig. 48], D). These are at first all alike, but later some of them become club-shaped, and develop at the end several (usually four) little points, at the end of which spores are formed in exactly the same way as we saw in the germinating teleuto spores of the cedar rust, all the protoplasm of the basidium passing into the growing spores ([Fig. 48], E, F). The ripe spores (E, sp.) are oval, and possess a firm, dark outer wall. Occasionally some of the basidia develop into very large sterile cells (E, x), projecting far beyond the others, and often reaching the neighboring gill.
Similar in structure and development to Coprinus are all the large and common forms; but they differ much in the position of the spore-bearing tissue, as well as in the form and size of the whole spore fruit. They are sometimes divided, according to the position of the spores, into three orders: the closed-fruited (Angiocarpous) forms, the half-closed (Hemi-angiocarpous), and the open or naked-fruited forms (Gymnocarpous).
Of the first, the puff-balls ([Fig. 49]) are common examples. One species, the giant puff-ball (Lycoperdon giganteum), often reaches a diameter of thirty to forty centimetres. The earth stars (Geaster) have a double covering to the spore fruit, the outer one splitting at maturity into strips ([Fig. 49], B). Another pretty and common form is the little birds’-nest fungus (Cyathus), growing on rotten wood or soil containing much decaying vegetable matter ([Fig. 50]).
Fig. 50.—Birds’-nest fungus (Cyathus). A, young. B, full grown. C, section through B, showing the “sporangia” (sp.). All twice the natural size.
In the second order the spores are at first protected, as we have seen in Coprinus, which belongs to this order, but finally become exposed. Here belong the toadstools and mushrooms ([Fig. 51], B), the large shelf-shaped fungi (Polyporus), so common on tree trunks and rotten logs ([Fig. 51], C, D, E), and the prickly fungus (Hydnum) ([Fig. 51], G).