  In the quasi two-dimensional GaAs/AlGaAs system, we investigate the effect of
rotating \textit{in-situ} the electric field of linearly polarized microwaves
relative to the current, on the microwave-radiation-induced magneto-resistance
oscillations. We find that the frequency and the phase of the photo-excited
magneto-resistance oscillations are insensitive to the polarization. On the
other hand, the amplitudes of the magnetoresistance oscillations are remarkably
responsive to the relative orientation between the microwave antenna and the
current-axis in the specimen. The results suggest a striking
linear-polarization-sensitivity in the radiation-induced magnetoresistance
oscillations.
