Streak photographs of the radial motion of vaporized electrode material in a flash X-ray (FXR) discharge indicate successive constrictions of the metal vapour cloud existing just outside the anode. Such a constriction may give rise to the anode vapour jet earlier observed in axial streak photographs of the discharge. Calculations show that the anode vapour production is sufficiently high to supply the discharge column behind the jet front with "new" vapour.