Unknown invertebrates?

Unknown invertebrates?

Observation - Unknown invertebrates?. Description: Small white spongy things underneath a flat brown disk all over a Field Maple tree next to a main road. At first I thought they were some sort of gall but on closer inspection they appeared as described.

Small white spongy things underneath a flat brown disk all over a Field Maple tree next to a main road. At first I thought they were some sort of gall but on closer inspection they appeared as described.