I think what happens is that we are seeing the mold at work. The visible part of the mold are the extensions that sporulate. Underneath, it's a white or colorless fabric of mycelium. So you inoculate and the molds are evenly distributed, start forming the mycelium, but without oxygen they can't finish the cycle. It's kind of how mushrooms only grow when the temperature and humidity and season is just right. Underneath, the mycelium mat is alive, but you don't see it up above.