Zones of ring shake and the tangential surfaces of such fractures were examined using light microscopy. The shakes occurred predominantly in bands containing abnormally large amounts of axial parenchyma, traumatic parenchyma and/or vessels. These cells, of low Runkel ratio, usually separated by some form of transwall failure, exposing the cell lumen. The failure thus followed a path entailing minimal fracture of actual cell wall substance. The zones of abnormal tissue are probably formed in response to cambial injury and/or environmental stress.