Hyphae are advancing into fresh media. The branches are arranged to give the most effective colonization and utilization of the substrate, and the growth of the hyphae is oriented to avoid the other hyphae. The mechanism by which this occurs is unknown, but probably relates to food gradients and toxin gradients. The productive zone . Here the major increase in biomass occurs.
Aerial mycelium is formed, and the hyphae thicken.
The fruiting zone . Biomass gain has ceased, and spores are formed. This is equivalent to the stationary phase of batch culture. Ageing zone . Vacuolate or empty hyphae are present, autolysis occurs.