Mechanism of formation of spiral grain in Aesculus stems: dissymmetry of deformation of stems caused by cyclic torsion

The reversibility of deformation of young (3-10-year-old) Aesculus hippocastanum stems was investigated after subjecting them to alternate torsion to the right and left as well as the orientation of the microfibrillar helix in the main S2 layer of the secondary cell wall in fibres. The studies demonstrated that residual torsions to the right are larger than to the left. The orientation of the fibrillar helix is always Z-wise. The dissymmetry of the mechanical properties of the stem may be responsible for the formation of Z (right-oriented) spiral grain in the stem of a tree undergoing torsions in various directions under the action of winds