The threshold power for stimulatedBrillouinscattering has been measured from 5° to 300°K in crystalline and fused quartz. There is only a small dependence on temperature. Further threshold measurements in 10 different substances show that instead the threshold depends on the photoelastic properties of the medium. Both facts were predicted by Kroll's dynamical theory. The threshold for stimulatedRamanscattering, however, may be strongly temperature dependent as demonstrated for calcite.