Xylogenèse chez les Dicotylédones arborescentes. II. Evolution avec l'âge des modalités de la réactivation cambiale et de la xylogenèse chez le Hêtre et le Chêne

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Abstract
Cambial reactivation and xylogenesis were studied in young oaks (ring-porous trees) and young beeches (diffuse-porous trees). A basipetal gradient of xylogenesis is present in the majority of young oaks (5-10 yr old) and in all young beeches (8-14 yr old), during the 1st weeks following cambial reactivation. Cambial reactivation proceeds downwards in young beeches at the rate of .apprx. 6 cm a day. The study of cambial cell differentiation in young disbudded trees shows that buds are indispensable for reactivation in beeches, whereas they are not necessary in the case of oaks, except for their 1st-yr shoots. Decapitation and disbudding prevent xylogenesis in young beeches, but they do not in the lowest part of old beeches. The simultaneous cambial reactivation, which occurs in oak axes > 1 yr old, appears between the 15th and the 30th yr in beech trunks; it bears no relation to the growth of terminal buds and to the basipetally progressing cambial reactivation of the branches.