The spores land on a place where they can turn into a new mold, and begin to grow. They very quickly start making "hyphae", small tendrils that look like roots. Hyphae are not roots, but part of the mycelium. The mycelium is the main part of the mold, and grows inside the bread. Black bread mold grows fast when the temperature is higher than 15 degrees Celsius and lower than 20C.