The acoustic characteristics of 111 kinds of leaves were determined using longitudinal ultrasonic waves (LUW) passing through the leaves suspended in water. The phase velocity of LUW in the leaves correlated with their thickness (r = 0.776). In leaves LUW wavelengths were almost equal to leaf thickness (r = 0.720). On the other hand, the group velocity did not correlate well (r = 0.210). The more delayed the phase of the transmitted wave, the greater the phase velocity, i.e. phase delay correlates with higher viscosity. The velocity increased as the frequency increased between 1.2 and 1.9 MHz, suggesting development of rigid reticular tissues. The propagation velocities of all the leaves were smaller than that (1497 m/s) of pure water. We therefore believe that the negative thickness and velocity dependencies of the attenuation coefficients are intrinsic characters of leaves, associated with the tissue's morphology.
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