Pattern of ray arrangement on cross section of bark of Aesculus

The arrangement of rays within the phloem and rhytidome was studied in Aesculus stems. It was found that on the cross section most rays in the stem deviate in Z-direction, that is to the right from the geometric radius. The mechanism of Z-arrangement of the rays may be as follows: owing to the action of wind on the crown torques arise causing the torsion of the wood core. The dissymmetry of the mechanical properties of the Aesculus wood core leads to accumulation of residual Z-torsion, and as consequence of this wood core torsion to the right occurs when seen from above. In the course of this torsion the soft phloem layers lying between the column and the rigid shield of the outer tissues (rhytidome and outher sclerified phloem layers) are drawn by the core and this results in their deviation to the right in respect to the geometrical radius.