"Although the spores are normally the propagative bodies and undoubtedly serve in the open for the distribution of the species, growers cannot employ these directly in the production of mushrooms. In fact it is difficult to germinate them in the laboratory...Under certain favorable conditions each of these minute cells is, however, capable of germinating and producing first a germ tube, ultimately a filamentous or threadlike growth, known as the mycelium. This mycelium arises from the first small germ tube by subsequent branching and continued ramifications, and under favorable conditions it grows until the rapidly elongating filaments penetrate the substratum in every direction. The growth of the mycelium in any suitable substratum yields a characteristic "spawn," and "spawn" refers merely to this phase of the mushroom growth in visible or extensive quantity. It is appropriately called the vegetative phase. Spawn may also be produced from fragments of the living tissue, if pure culture methods are employed..."