The radial direction of wood is reinforced by an additional tissue called rays. These rays are one of the reasons for the anisotropy of wood in the transverse plane. In this paper the influence of rays on the mechanical properties like tensile strength as well as on fracture mechanical parameters like critical stress intensity factor and specific fracture energy is shown. By investigating two deciduous tree species with a similar wood structure in general but a different ray characteristic in particular the importance of this radial reinforcement of the wood structure could be demonstrated. The relevance for the living tree is discussed.