We examine spectral time-series of two lower-chromospheric lines (N I 1319 AA and C II 1335 AA) observed with SUMER instrument on the SOHO spacecraft. We point out differences between (intensity and velocity) power spectra of network and internet work regions and argue that the behaviour resembles that of CaII power spectra. No Significant phase differences are found between the intensities of both lines. However, when phase spectra are averaged along the slit there is some evidence that the CII intensity lags that of NI by 16 sec near 3 mHz. Intensity power spectra of CII are affected at higher frequencies by streams of emitting structures. Using contrast-enhanced time slices we show that 1) there exists a grain-like pattern which is found in both network and internet work regions; 2) streams of supersonically moving structures probably outline a wave interference pattern; 3) the sizes of structures observed in NI are smaller than when observed in CII. At various points our findings disagree with earlier results from SUMER. A cookbook formalism is presented to derive confidence levels for power, phase, gain and coherency spectra.