helical grain

Grain that is helical rather than axial, arising from a genetic predisposition (it is often seen in sweet chestnut; Castanea sativa) or in response to a torsional stress in a prevailing direction, for instance due to the force of the wind on an asymmetrical crown.

axial, axis,
helical failure,
interlocked grain,
timber defect,
torsion, torque

This definition is abridged from A – Z of tree terms: A companion to British arboriculture.
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