Brynna Woods oak leaf 2sep2013

Brynna Woods oak leaf 2sep2013

Observation - Brynna Woods oak leaf 2sep2013 - UK and Ireland. Description: Q. robor leaf with unknown pustules on underside. Pustules upto 4mm diameter regular circles.Tan with lighter margin and peak. Hollow underneath. Attached to surfacr of leaf - easy to detach. X10 magnification shows hairs and darker 'scales'. Any ideas

Q. robor leaf with unknown pustules on underside. Pustules upto 4mm diameter regular circles.Tan with lighter margin and peak. Hollow underneath. Attached to surfacr of leaf - easy to detach. X10 magnification shows hairs and darker 'scales'.
Any ideas please!