What are mycelium?

Mycelium refers to the network of thread-like structures known as hyphae that compose the main body of a fungus. These microscopic threads spread out and can penetrate various substrates, helping the fungus to absorb nutrients. This structure is fundamental to the life cycle of fungi, as it plays a critical role in decomposition and nutrient cycling in ecosystems.

The other choices describe different aspects or forms of fungi but do not accurately define mycelium. For instance, large visible fruits of fungi would be fruiting bodies, like mushrooms, which arise from the mycelium but are not the mycelium itself. Solid structures for reproduction relate to other fungal components, such as spores or certain reproductive structures, while liquid forms of fungal spores do not represent the mycelium, which is primarily a solid, fibrous structure.