There are some key things to understand the difference between spawn and spores and a basic understanding of a mushroom is needed. As a mushroom matures throughout its life cycle, the mushroom cap opens and exposes its gills. Mushroom spores are microscopic spheres produced in the gills that can be thought of as the “seeds” of a mushroom. The gills of a mushroom are like manufacturing powerhouses – producing incredibly large numbers of spores to spread into the external environment. In some species, mushroom spores can be produced in numbers of up to 40 million per hour! As spores germinate and grow, a thread or wool-like mycelium develops which is used by laboratories to develop mushroom spawn using a medium such as grain. The mycelium/grain mixture is what is usually referred to as mushroom spawn, which can then be used to ‘seed’ a mushroom compost or substrate.