Can anybody explain the conical growths on the leaf in the picture? This was a "show and tell" from a child so I don't have any information on what kind of tree it came from. The growths are about 5mm high Bob
Galls produced by Eriophyes mites, most likely Eriophyes tiliae. They don't cause any significant harm. The tree is a Common Lime Tilia × europaea.
