There are a number of these interesting fungi growing on dead wood at the bottom of our garden, Its' scientific name is Daldinia concentrica, but it has the common names of Cramp Balls or King Alfred's Cakes. An unusual fungus, in the form of very hard black balls growing on dead or dying Ash branches. Each fruit body is 1-5cm in diameter. If you can cut one open you will make out concentric growth rings. In the past it was used to treat cramp, and the second name refers to the time King Alfred burnt the cakes, so do not attempt to eat them. They are not poisonous, but due to the texture I think your teeth would suffer more than your stomach!