def plot(self, phi, r, **kwargs):
        """Add a data series to the plot.

        :param phi: array containing phi-values, should be in degrees
                    (or radians).
        :param r: array containing r-values.

        For further options see the plot function of the super class.

        """
        if self.use_radians:
            phi = np.degrees(phi)
        super(PolarPlot, self).plot(phi, r, **kwargs)