Xylogénèse chez les Dicotylédones arborescentes. V. Formation du bois de tension et transport de l'acide indole acétique tritié chez le Hêtre

Upper stems of young beeches (Fagus silvatica L.) were bent into Jaccard loops in May. If they stayed on the tree, they produced a wide arc of extreme tension wood on the upper side of the loop, which contained numerous gelatinous fibers, few vessels, and little axial parenchyma. On the lower side of these loops, xylogenesis was nearly stopped. If bent stems were removed from the tree, xylogenesis was far less asymmetric: the wood formed on the upper side contained normal vessels and axial parenchyma, but also gelatinous fibers; on the lower side, the wood was normal. Transport and metabolism of 3H-labelled indole acetic acid was studied in both models. In intact loops left on the trees, lateral auxin transport took place mainly towards the lower half of the stem. In isolated loops, no preferential direction could be detected for lateral auxin transport. Extreme tension wood differentiation on the upper side of a bent stem requires the intervention of correlative factors, not only from buds, but also from the base of the tree, which particularly influence lateral downward transport of auxin.