Some varieties, called _true_ parasites, develop in uninjured trees, while others, called _wound_ parasites, can penetrate the tissues of trees, only where a cut or injury makes a suitable lodgment for the spores. Some fungi attack only a single species of trees, others whole genera; some attack only conifers, others deciduous trees, while a few attack trees of nearly all kinds alike. Fungal spores when brought in contact with a wound on a tree or other suitable place, and provided with suitable conditions of growth, germinate, penetrate the tissues and grow very rapidly. These spores send out long threads or filaments which run thru the cells lengthwise and also pierce them in all directions, soon forming a network in the wood called the mycelium. Rotting, in a large number of cases, is due to the ravages of fungi. This sometimes shows in the color, as the "red rot" of pine or the "bluing" of ash. Sometimes as in "pecky" or "peggy" cypress, the decayed tracts are tubular. More commonly the decayed parts are of irregular shape. The decay of wood is due to the ravages of low forms of plant life, both bacteria and fungi. A few of the more destructive forms may be noted. _Trametes pini_ (Brot.) Fr. Foremost among the timber destroying fungi is the large brown "punk" or "conch" found in its typical development on the long-leaf and short-leaf pines, _Pinus palustris_ and _Pinus echinata_, Fig. 81. The fruiting bodies form large masses which grow out from a knot, oftentimes as large as a child's head. They are cinnamon brown on the lower surface, and much fissured and broken, on the black charcoal-like upper surface. This fungus probably causes four-fifths of the destruction brought about by the timber destroying fungi. It occurs on most of the conifers in the United States which have any value as lumber trees, and brings about a characteristic white spotting of the wood, Fig. 82, which varies with the kind of tree attacked. (Von Schrenk, _Agric. Yr. Bk._, 1900, p. 206.) [Illustration: Fig. 81. A "Conch," the fruiting body of _Trametes pini_, on Sugar Pine. [_Agric. Year Book, 1900_, Pl. XXII, Fig. 2.]] [Illustration: Fig. 82. Effect of Fungus. (_Trametes pini._) _U. S. Dept. Agric._] [Illustration: Fig. 83. "Shelf" Fungus on Pine. _a._ Sound wood; _b._ Resinous "light" wood; _c._ Partly decayed wood or punk; _d._ Layer of living spore tubes; _e._ Old filled-up spore tubes; _f._ Fluted upper surface of the fruiting body of the fungus, which gets its food thru a great number of fine threads (the mycelium), its vegetative tissue penetrating the wood and causing its decay. [_After Hartig._]] Of the shelf fungi, which project like brackets from the stems of trees, and have their pores on their under surfaces, one of the commonest in many localities is the yellow cheese-like _Polyporus sulphureus_, Fig. 83. This is found on oak, poplar, willow, larch, and other standing timber.