Answer:
By the time you see a bracket forming on a tree or piece of wood, the fungus that produced it has been growing on the wood for a while. Microscopic threads of the fungus, called hyphae (HI-fee) can infect a tree or log, and grow, producing wood-degrading enzymes which it secretes, breaking down the wood, and then absorbing the broken down wood bits. This is where the fungus gets its' nutrition.