The origin of moving striations has been investigated by measurement of striation propagation at a sharp change in tube diameter, by study of the relationship between anode spot oscillations and moving striations, by observation of anode spot oscillations at the cutoff current for moving striations, by use of an auxiliary discharge to suppress anode potential oscillations, and by study of a striation system isolated from electrodes. The experiments indicate that: (a) the striation frequency, velocity, and wavelength all change discontinuously at a change in tube diameter; (b) visible spot oscillations are accompanied by oscillations in discharge potential, and exist unchanged above the critical current for disappearance of moving striations; (c) anode oscillations and anode spots may be suppressed by operation of an auxiliary discharge to the anode; (d) the striation frequency synchronizes to an applied oscillation at the anode, provided the applied frequency is close to a small integral multiple of the natural striation frequency; and (e) a striation system can be maintained in a vessel separated from the electrodes by narrow tubes operated above the local critical current for moving striations. No oscillations can be detected in the isolating regions either photoelectrically or with electrostatic probes.It is concluded that: (1) anode oscillations and moving striations are independent phenomena; and (2) moving striations do not constitute the response of the discharge to an external perturbation, but appear to result from a local instability in the positive column.