Many fungi spend much of the year as extremely thin, elongated tubes known as hyphae. Collectively, the hyphae make up the mycelium of the fungus. Hyphae are often invisible to the naked eye, but sometimes become visible if they grow prolifically or become interwoven to form cords.
Fruiting bodies are produced to enable the formation and release of spores, thus allowing the dispersal of the fungus over greater distances than would be possible by vegetative growth alone. They usually enlarge very rapidly, becoming engorged with water in just a few hours. This hydraulic pressure is designed to push the fruiting body through the soil so that it can be exposed to the air to release its spores, but in some fungi (e.g. puffballs) it can be so great that it can damage tarmac and lift paving slabs.
Most of the fungi that produce fruiting bodies on dead wood are saprophytic species. However, the pathogenic fungi that attack and kill live wood also produce their fruiting bodies on dead wood and stumps. These pathogens include honey fungus (Armillaria spp.), silver leaf (Chondrostereum purpureum) and Ganoderma species bracket fungi. If there is any concern that a fruiting body on a tree stump or dead branch might be that of a pathogenic fungus it would be prudent to have it identified.
Finally, a specialised group of organisms called mycorrhizal fungi live in a close, beneficial association with plant roots (mycorrhiza translates as ‘fungus-root’). These fungi enhance the plant’s uptake of water and nutrients, in turn obtaining some nutrition from the plant. Mycorrhizal fungi will often produce fruiting bodies in the vicinity of the roots.