Effet de la durée d'application d'un stimulus gravitationnel sur la formation de bois de tension et de bois opposé dans de jeunes pousses de peuplier (Populus euramericana cv 'Ghoy')

Young shoots of Poplar Ghoy have been inclined artificially during increasing periods to induce the formation of tension and opposite wood tissues as reaction to the gravitational stimulus. The shoots are able to react to an extremely short stimulus according to the scale of the normal growing season. After a presentation time of only 6 hours, the whole of the shoots present an opposite wood arc. However, on the upper face, it takes between 24 and 48 hours, for the shoots to feel the modification of their equilibrium state and start producing tension wood. After 48 hours of latent period, formation of gelatinous fibres can be observed on the upper face of the stem. The increase duration of the stimulus influences the quantity of gelatinous fibres and the arc angle of the tension wood. On the lower face, the opposite wood fibres are produced at a slower rate, causing a pith eccentricity. The shoots will return to the stand-up position after being submitted to a stimulus of approximately 4 to 8 days.