Rather a strange New Year picture I guess! These strange little nodules occur on several types of tree but mostly beech I think. They apparently happen when a bud on the tree is "aborted" and becomes detached from the main stem and sits in the bark until it eventually rots away. They can grow quite big - large potato sized - and they are prized by wood carvers because of their interesting graining. I've only ever seen small ones like these - but if I ever find an interesting one I might remove it and investigate!
