What is this on my live oak tree leafs?

[zene55]

Any idea what these are?

 

[Clint S]

Oak gall, Some sort of insect has laid eggs under the bark of the tree and the "gall" is a response.

 

[woodchuckie]

I have a tree that has things similar to those. They turn from green to brown and feel like a dried leaf. When I open them it looks like a seed. The tree also produces acorns.

 

[Gale Hawkins]

I have been seeing them on oak for the last 55 years but never knew what they were.