Order 3. Tuberaceæ, Truffles. The Fungi belonging to this order are entirely subterranean. The mycelium is filamentous, and partly parasitic upon the roots of plants, especially trees, in its neighbourhood; it is then known as Mycorhiza. The fruit-body is relatively large, in some cases about the size of a hen’s egg. Internally it is traversed by a number of winding passages (Fig. [113] a), the walls of which are coated with the asci. The asci (b) contain only a small number of spores, and these are set free by the putrefaction of the fruit-body. Conidia are unknown.
Fig. 113.—Tuber melanosporum: a fruit-body (nat. size), a portion having been removed to show the internal structure; b an ascus with ascospores.
Tuber melanosporum, T. brumale, T. æstivum, and other species are edible. Terfezia leonis and Choiromyces mæandriformis are also edible. The Truffles are always found in woods and under trees, and disappear when these are destroyed. France and Italy produce the best and the largest number of Truffles, which are hunted by specially trained dogs and pigs.
In Elaphomyces (Stag-Truffle) the fruit-body has a corky external layer, and is inedible. Some of the species are found in this country. E. granulatus is parasitic on the roots of the Fir.
Family 3. Pyrenomycetes.
In this family the hymenium is enclosed in small fruit-bodies, perithecia (Fig. [120] b), which appear to the naked eye as small dots. In shape they resemble a globe or a flask with a narrow mouth, through which the spores are ejected (peronocarpic ascocarps). Different kinds of reproduction—conidia, pycnidia (chiefly with microconidia), chlamydospores, and perithecia—are found in the same species. The various stages in the life-history of these Fungi are so dissimilar, that formally they were considered to be different genera. Ergot furnishes a very good example.
Fig. 114.—A small portion of an ovary attacked with Claviceps purpurea (Sphacelia).
