Question
I have what looks like a bur Oak tree with light green worm like extentions growing out of the leaves, mostly down the center. It seems to be some sort of fungus on this 100 year old tree.What is it and can it be treated?

Answer
The short story is that certain behaviors (such as feeding or laying eggs) of certain insects cause plant cells to begin multiplying like crazy until something is developed a lot like a plant tumor. This tumor-like growth is called a gall, and there is simply an amazing variety of galls. Moreover, very often it is easier to determin the presence of an insect by the gall it has formed, than it is to find the insect itself. Typically, when larvae develop inside these galls they eat the gall's tissue, which may be much softer and more nutritious than regular plant tissue. Often galls also provide protective homes for the larvae or even adult insects.

The galls themselves will not harm the overall health of the tree although they can look bad. Leaf galls may cause the leaves to drop permaturely. There are many types of these wasps some attack the twigs and others the leaves. Control is not usually needed and has to be timed with the wasp presence and not the galls themselves. Here is a web links  gall wasp that discuss the wasps and control measures.I would really not worry about the galls.  http://www.ces.ncsu.edu/depts/ent/notes/O&T/trees/note05/note05.html