Résumé
In order to understand what is controlling the magnitude of the longitudinal growth stress in tension wood, an experiment was carried out on poplar tension wood (Populus I4551). Results show that (a) in the region where growth strain value is between 610 and 816 µstrain gelatinous fibres are common, above the value between 1540 and 1935 µstrain almost all fibres contain gelatinous layers; (b) the amount of fibres, the amount of fibres with gelatinous layer (G-Fibres), per unit of tissue area, and the thickness of the gelatinous layers in fibres control mostly the magnitude of growth stress; (c) other possible factors contributing to growth stress are the lignification, crystallinity and microfibril angle in the fibres without G-layer within the region partly containing G-fibres and in G-layers themselves.