by the tree's own defence mechanisms, until something occurs to weaken the tree. Fire, drought and suppression by other trees are common causes of such stress. In most infections there is only one fungal individual present, but occasionally several individuals may be isolated from a single tree, and in these cases it is possible that the birch bracket fungus entered after something else killed the tree. These fungal "individuals" can sometimes be seen if a slice of brown-rotted birch wood is incubated in a plastic bag for several days. This allows the white mycelium of the fungus to grow out of the surface of the wood. If more than one individual dikaryon is present, lines of intraspecific antagonism form as the two individual mycelia interact and repel each other. The fungus can harbor a large number of species of insects that depend on it for food and as breeding sites. In a large-scale study of over 2600 fruit bodies collected in eastern Canada, 257 species of arthropods, including 172 insects and 59 mites, were found. The fungus is eaten by the caterpillars of the fungus moth Nemaxera betulinella. Old fruit bodies that have survived the winter are often colonized by the white to pale yellow fungus Hypocrea pulmonata. Research on chemical constituents Fomitopsis betulina has been widely used in traditional medicines, and has been extensively researched for its phytochemistry and pharmacological activity. Phytochemicals include phenolic acids, indole compounds, sterols, and triterpenes. Agaric acid found in the fruit body of the fungus, is poisonous to the parasitic whipworm Trichuris trichura. The fungus was carried by "Ötzi the Iceman" – the 5,300 year old mummy found in Tyrol, with speculation that the fungus may have been used as a laxative to expel whipworm. Uses The velvety cut surface of the fruit body was traditionally used as a strop for finishing the edges on razors, and as a mounting material for insect collections. It has also been used as tinder and anesthetic. See also Fomes fomentarius another fungus carried by Ötzi the Iceman References Fomitopsidaceae Fungi described in 1788 Medicinal fungi Fungi of Asia Fungi of Europe Fungi of North America Inedible fungi Parasitic fungi Taxa named by Jean Baptiste François Pierre Bulliard