The body of a fungus is called the mycelium. Mycelium is a network of thread-like structures known as hyphae. These hyphae grow through the substrate, which can be soil, wood, or other organic materials, and absorb nutrients for the fungus. While many people are familiar with mushrooms, which are the reproductive structures of fungi, mycelium is actually the main part of the organism and plays a crucial role in its survival and growth.