The mass of hyphae that grows into bread to digest is called a mycelium.

Here's why:

* Hyphae: These are the long, branching filaments that make up the body of a fungus.

* Mycelium: A mycelium is a network of interwoven hyphae that forms the main body of a fungus.

The mycelium grows into the bread, secreting enzymes that break down the starches and sugars in the bread. The fungus then absorbs these nutrients for its own growth and reproduction.