Oak Leaf

What is this fungus-looking thing on the oak tree leaves? It is on EVERY LEAF!?

I don’t think it’s eggs because when we scraped one open it looked like the inside of a green apple.
And the tree is really old and HUUUGEE.

http://tinypic.com/r/34j23ci/3

http://tinypic.com/r/k97vir/3

are galls a fungus ?

They are immature galls caused by parasitic wasps (not fungus) [...]