Mycelium (often used as a mass noun, but also with plural mycelia) is the root-like part of a fungus, forming complex branching structures that spread through the growing medium, often soil. Mycelium networks describe these branching structures, often those of multiple individual fungi; they are able to carry electrical signals, transport water and nutrients, and absorb from and secrete nutrients into the growing medium. Mycelium networks perform various essential functions in ecosystems such as contributing to soil organic carbon, providing a food source for invertebrates, facilitating nutrient absorption by plant roots and facilitating decomposition.