embryonic tissue

Knopper gall Andricus quercuscalicis on English Pendunculate or Common Oak Quercus robur.   Illustrations shows  mature gall, formed from acorn embryonic tissue thanks to the gall wasp

Knopper gall Andricus quercuscalicis and Oak apple gall Cynips quercusfollii on English Pendunculate or Common Oak Quercus robur