Since mushrooms are just reproductive structures, you wonder what they are the reproductive structures of. Microscopic spores fall from the pores and gills of mushrooms such as those pictured above. If environmental conditions are just right, fungal hyphae (HI-fee, the plural of "hypha") emerge from the spore -- like the sprout emerging from a seed. These hyphae form a webby mass of typically white, interwoven, threadlike filaments known collectively as mycelium. Each individual, threadlike filament of the mycelium is known as a hypha (HI-fah), plural hyphae (HI-fee). This mycelium composed of hyphae does the organism's day-to-day work of breaking down and acquiring the fungus's food from humus in the soil, or decaying wood or some other substance. In other words, though usually mycelium isn't even noticed by most people, it's actually the fungus organism's body. Then when conditions are right the mycelium mass forms a budlike structure someplace and from this emerges the mushroom. The mycelium does the fungus's work, and the mushrooms enable to fungus organism to reproduce by producing spores.