Mushrooms are an easy-to-spot sign of disease that may indicate root rot and a potentially unstable tree.

WSJ: Getting to the Roots of Your Trees' Stress

First, the atmosphere must be what is called potentially unstable.

CNN: The making of a nightmare tornado

With a new US president with very little if any knowledge of world politics and a potentially unstable domestic platform after the recent, highly political judgement reached by the American Supreme Court, the time has never been better for Europe to take up its historic responsibility to put its own house in order.

BBC: What future for the EU?

During the debate, the SDLP's Alex Attwood said clause 2 of the bill, which deals with justice powers potentially lapsing by May 2012 - the "sunset clause" - created an unstable situation.

BBC: Department of Justice Bill

Offshore deposits present a potentially enormous source of methane but also some environmental concern, because the underwater geology containing them is unstable in many places.

BBC: Production test