Of the irregular shaped fungi, one of the most destructive is a true parasite, _i.e._, one that finds lodgment without help, called _Polyporus annosus_ and also _Trametes radiciperda_, Fig. 85. It is peculiar in developing its fructifications on the exterior of roots, beneath the soil. Its pores appear on the upper side of the fructifications. It attacks only conifers. Its spores, which can be readily conveyed in the fur of mice or other burrowing animals, germinate in the moisture around the roots: the fine threads of "spawn" penetrate the cortex, and spread thru and destroy the cambium, extending in thin, flat, fan-like, white, silky bands, and, here and there, bursting thru the cortex in white, oval cushions, on which the subterranean fructifications are produced. Each of these is a yellowish-white, felt-like mass, with its outer surface covered with crowded minute tubes or "pores" in which the spores are produced. The wood attacked by this fungus first becomes rosy or purple, then turns yellowish, and then exhibits minute black dots, which surround themselves with extending soft white patches. (Boulger, p. 73.) [Illustration: Fig. 85. 1. Stump of Norway Spruce, with a sporophore of _polyporus annosus_ several years old; the inner portions of the stump wholly decayed. 2. Roots of a diseased spruce tree, with numerous small sporophores of _polyporus annosus_ attached. _Forestry Bulletin 22_, Plate XIII, Figs. 1 and 2.] Of the fungi which attack converted timber, the most important is "dry rot" or "tear fungus" (_Merulius lachrymans_), Fig. 86. It flourishes on damp wood in still air, especially around stables and ill ventilated cellars. It gets its name lachrymans (weeping) from its habit of dripping moisture. The fungus destroys the substance of the timber, lessening its weight and causing it to warp and crack; until at length it crumbles up when dry into a fine brown powder, or, readily absorbing any moisture in its neighborhood, becomes a soft, cheese-like mass. * * * Imperfectly seasoned timber is most susceptible to dry rot: the fungus can be spread either by its spawn or by spores, and these latter can be carried even by the clothes or saws of workmen, and are, of course, only too likely to reach sound wood if diseased timber is left about near it; but on the other hand dry timber kept dry is proof against dry rot, and exposure to really dry air is fatal to the fungus. (Boulger, p. 75.) [Illustration: Fig. 86. Portion of the mycelium of dry rot or tear fungus, _Merulius lachrymans_. This cakelike mass spreads over the surface of the timber. In a moist environment pellucid drops or "tears" distil from its lower surface: Hence its name. [Ward: _Timber_; Fig. 21.]]