563 PB 412 RICHARDS FUNCTION IN FREEZING TOLERANCE DETERMINATION WITH ELECTROLYTE AND PHENOLIC LEAKAGE TECHNIQUES

Freeze tests were performed on stem sections of Fraxinus americana, Lagerstroemia indica Magnolia gradiflora, Rhododendron `Red Ruffle', Zelkova serrata, and leaves of Magnolia grandiflora and Rhododendron `Red Ruffle' in the tinter and summer of 1993. Freeze injury was quantified using electrolyte and phenolic leakage techniques and compared to the lethal temperature range determined by visual method assisted by differential thermal analysis. Richards function was fitted to the electrolyte and phenolic leakage data by the modified Gauss-Newton method. The inflection point of the Richards function coincided with the lethal injury range for non-acclimated leaves, but overestimated the freeze tolerance for acclimated leaves and for both acclimated and non-acclimated stems. A proposed interception point of the lower asymptote and a line tangential to the curve inflection point provided an improved estimate of the lethal injury range in most of the species.

Decay of Temporary Threshold Shift in Noise

Groups of monaural chinchillas trained in behavioral audiometry were exposed in a diffuse sound field to an octave-band noise centered at 4.0 k Hz. The growth of temporary threshold shift (TTS) at 5.7 k Hz from zero to an asymptote (TTS ∞ ) required about 24 hours, and the growth of TTS at 5.7 k Hz from an asymptote to a higher asymptote, about 12–24 hours. TTS ∞ can be described by the equation TTS ∞ = 1.6(SPL-A) where A = 47. These results are consistent with those previously reported in this journal by Carder and Miller and Mills and Talo. Whereas the decay of TTS ∞ to zero required about three days, the decay of TTS ∞ to a lower TTS ∞ required about three to seven days. The decay of TTS ∞ in noise, therefore, appears to require slightly more time than the decay of TTS ∞ in the quiet. However, for a given level of noise, the magnitude of TTS ∞ is the same regardless of whether the TTS asymptote is approached from zero, from a lower asymptote, or from a higher asymptote.