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.)
Fig. 81. A "Conch," the fruiting body of Trametes pini, on Sugar Pine. [Agric. Year Book, 1900, Pl. XXII, Fig. 2.]
Fig. 82. Effect of Fungus. (Trametes pini.) U. S. Dept. Agric.
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.