STUDY ON THE GROWTH AND DEVELOPMENT OF THE COMMON ASH, FRAXINUS-EXCELSIOR, CULTIVATED UNDER CONTROLLED CONDITIONS

Under controlled conditions (14 h light : 10 h dark; 27 +/- 1 and 19 +/- 1 degrees C), common ashes, Fraxinus excelsior L., display a rhythmic growth. The average duration of the first growth flush is 106 days, followed by a phase of nonlengthening from 9 to 11 months, depending on individuals. This rhythm was materialized in the shoot organization. The end of each growth stage was characterized by progressively shorter internodes and by the presence of scales around the bud. Histological studies reveal that no leaf is preformed at the embryo stage and that the meristem activity carried on after the stem growth stops. The common ash growth rhythm is therefore not the direct consequence of the arrest of meristem activity. The nonlengthening phase is an apparent resting phase during which the initiation of new leaves carries on.