The heterogeneousness of the physical and mechanical properties of Eucalypts from plantations limits the utilization of this group of species for solid wood products. In effect, wood products manufacturers aim to process a material as homogeneous as possible in order to be able to propose standard quality products to their customers. The variations caused by juvenile wood have a morphogenetic origin; it corresponds to a progressive transition of wood structure from the young state to the adult one. This transition induces variations of properties on the radius or according to the age of trees; it is particularly significant for basic density. Tendencies observed are changing from the bottom to the top of the bole : - in the outer part of the stem, basic density and Young's modulus are both decreasing, - near the pith, both properties are increasing. This could mean that, at a given cambial age, the wood from the upper part of the stem would be "less juvenile" than the wood from the bottom. The study of wood variations inside the stems and according to the age of trees amounts to consider two types of wood juveniliy : the primary juvenility linked to the primary growth of the trees and the secondary juvenility linked to the secondary growth.