F. annosus produces conidia abundantly in culture but rarely under natural conditions. Sporophorea are formed on stumps and dying trees throughout the year provided that the humidity is sufficiently high. Spore discharge in the plantations may occur at any time of year, but slowa down or ceases during very dry weather. It takes place at low temperatures, ceasing only when sporophores freeze. In the laboratory, F. annosus basidiospores germinate in relative humidity exceeding 92 per cent. on freshly cut, unsterilized pine wood. Viability is lost rapidly in light at temperatures above 15°C. Under humid conditions F. annosus spores will infect freshly cut pine stumps. There is evidence that spores of F. annosus washed down into soil remain viable for at least a short period and that stumps covered with soil are infected from this source. F. annosus spores can infect stumps for only a few weeks after felling, colonization after a longer interval probably beingprevdnted by competing fungi. In stumps inoculated with a mixed suspension of F. annosus and Peniophora gigantea spores, Fomes at first colonized the wood but was soon replaced by P. gigantea. Other aspects of competition are discussed. The incidence of natural infection in stumps and the factors affecting it are discussed Growth rates of F. annosus on malt agar and in lengths of pine root are given. The fungus grows in stump roots at about 1 m. per year, and so closely approaches adjacent trees within a year of thinning the plantation: In large stumps, F. annosus may survive 15 or even 30 years after felling. Data are given which suggest that the infective capacity of stumps containing F. annosus is greater in alkaline than in acid mils, while replacement by other fungi is slower. Competition of F. annosus with other fungi during colonization of stumps is discussed. The parasite can grow along roots already occupied by certain fungi but not along roots containing others. The probable course of succession in stumps rotted by F. annous is described.