Balls on Oak Trees

[SeniorCitizen]

Does anyone know the purpose of Balls on Oak trees? As kids we always called those ink balls because of the natural ink appearing fluid inside when cut open.

 

[Tetters]

Those are oak apples @SeniorCitizen, they are galls formed by a wasp that lays her eggs on a bud.

 

[Sheal]

You beat me to it @Tetters .

This may be of help. The site is a bit slow in opening.

Oak gall wasps / RHS Gardening