Why do mushrooms ...

[JeremyBrowne]

In article <4tp0ad$5c3 at sjx-ixn4.ix.netcom.com>
           allai_x at ix.netcom.com(Docktor "Docktor Crow Goodfellow " writes:

> A friend of mine said that some mushroom grow in rings of perfect
> circles (that is, multiple mushrooms forming a circle).  Is this true? 
> For all mushrooms?  For some?  If it is true, why is it so?

Some fungi do indeed grow in rings, but perfect may not be quite accurate!
Two species known for producing rings are Tricholoma Gambosum 
(St. Georges Mushroom - also known as Calocybe Gambosum or Lyophyllum georgii)
and Marasmius Oreades (Fairy Ring Champignon).

Myths ascribe the rings to fairies, witches, the devil dragons etc. but:
"Fairy rings" (typically in three concentric rings) are caused by mycelium  
of fungi growing from a central starting point. As the mycelium grows, 
it produces changes in the organic matter of the soil. Ammonia is 
liberated and produces nitrates or ammoniacal salts, manuring 
the vegetation, & stimulating its growth. 

As the mycelium increases, it fills the air spaces in the soil so that rain-
water has difficulty in percolating, at a time when the increased vegetation
is making greater demands on the available water. This causes localised 
drought and the plants die, leaving a bare circle. The part behind dies 
off and water can now panetrate the soil and the dead fungus becomes food
for the plants which invade the bare area and so on. Obviously the ring 
widens year on year.

-- 
Jeremy Browne, Hampshire, UK
Shaking Hands BBS, Fidonet 2:252/160