There is a myth that immediately after heavy rains in forest, mushrooms appear in large number and make a very large ring or circle, which may be several metres in diameter. These are called as "fairy rings". Can you explain this myth of fairy rings in biological terms ? Discuss the mycilial structure in Agaricus and its soil borne nature. 

Explanation

The fairy rings form as the mycelium of the mushroom fungus spreads in the soil from a central point.
It grows peripherally, so that the younger hyphae will appear almost in a circle.
The mycelium of mushrooms absorbs nutrients from the ground.
When nutrients at the centre get exhausted they grow in diameter and form a circle.
The ring grows in diameter every year which are actually fruiting bodies of the fungus.
This is called .Fairy Ring. especially in Europe.