The mushroom you can see is only a part of the mushroom plant. This is like the fruit of other plants. Most of the mushroom plant is hidden below the soil.

The whole of the mushroom is made up of threads called HYPHAE packed so closely together they form a solid mass. This gives the shape we associate with mushrooms and toadstools.

The part of the mushroom or toadstool above the ground is really the FRUIT  or the SPORE BEARING part.

Beneath the soil there is a dense mass of these whitish threads or HYPHAE.

At times little buttons begin to grow on the threads. These grow rapidly. Sometimes they grow out of the ground on a single night.