Ultrasonic velocities propagating in wood as an orthotropic solid and the velocity surface in wood [17]. Legend: (a) Velocity surface of curly maple wood deduced from experimental values measured using broadband transducers that have a central frequency of 1 MHz for P waves and S waves in the through transmission technique ([17], Fig. 5.4, p. 67). Ultrasonic velocities in an orthotropic solid and in wood: V₁₁ = V_LL, V₂₂ = V_RR, V₃₃ = V_TT, for P waves and V₄₄ = V_RT, V₅₅ = V_LT, V₆₆ = V_LR, for S shear waves ([17], Fig. 2.1, p. 21); (b) Anisotropic symmetry axes and structural anatomic elements of softwood and hardwoods ([18], Fig. 4).