In the present experiment thermal excitation of free holes is clearly evident on the absorption spectra when the temperature is above 1 0 K and a single cyclotron line exists above 30 K. At a temperature of 4.2 K, only impurity absorption lines are exhibited.The paper quoted in /2/ deals mostly with absorption lines measured at 4.2 K. Moreover, the authors claimed that "The results a s well as the others not presented give practically the s a m e values of the cyclotron effective mass, for a given configuration, independently of magnetic field, l a s e r wavelength, and temperature" . Contrarily, the present experiment shows that for a given configuration of the magnetic field, the lines measured at a low temperature do not scale with the magnetic field for different excitation energies. This means that the lines, i f interpreted as cyclotron lines, give a drastic difference in effective cyclotron m a s s when changing the excitation wavelength radiation.