" Some mycelium will actually insinuate itself into the grain of trees, taking up residence and forming a symbiotic relationship with the tree. Stamets believes the mycelium functions as a kind of immune system for its arboreal host, secreting antibacterial, antiviral, and insecticidal compounds that protect the trees from diseases and pests, in exchange for nourishment and habitat. "

― Michael Pollan , How to Change Your Mind: What the New Science of Psychedelics Teaches Us About Consciousness, Dying, Addiction, Depression, and Transcendence