TENSION wood, the reaction wood of angiosperms, is usually formed as a morphogenetic response to geotropic and other orientation movements of stems and branches. In general it is formed on the upper side of leaning stems and its formation is thought to be a regulatory response, maintaining the stems and branches in specific orientations. Anatomically, tension wood is characterized by fibres with a conspicuously thickened inner layer of the cell wall, the gelatinous layer, which is unlignified or only partially lignified. In addition there is a marked reduction in the size and number of vessels in comparison with adjacent normal wood1. An eccentricity of growth is frequently associated with tension wood formation, with wider growth rings evident on the tension wood side2.