I was reading in The Discovery News website that it has been discovered that some plants generate an aspirin-like chemical when they are under stress.  The article goes on to explain that this discovery was an accidental one, it was discovered near a walnut grove.  Scientists were monitoring the air (it doesn’t say why) when they discovered that the trees were emitting this gas.  Then the article goes on to explain that aspirin was originally made from the bark of willow trees.  I didn’t know that!  You learn something new every day!