The formation of soot in premixed, flat, low-pressure acetylene oxygen flames is studied by measuring volume fractions of soot, particle number densitiesand particle sizes by means of laser light scattering and extinction. Additionally, flame temperatures and composition are measured employing the Kurlbaum method and mass spectrometric analysis of mcrioprobe samples, resp. The flame are seeded with CsCl and compared with unseeded flames providing the same soot volume fraction. The respective seeded and unseeded flames scarcely differ in flame properties, such as flame temperatures or “chemical environments” of the soot particles. The seeded and unseeded flames show similar soot appearance rates at different specific surfaces of soot particles. The specific surfaces of soot particles in the seeded and unseeded flames differ, because the soot particles in the seeded flames are prevented from coagulation by their electrical charges. The independence of surface growth rate on the specific of the soot particles hints to a growth mechanism with the rate determining steps in the “pre-growth” reactions. A qualitative picture is derived from a mechanism for growth and cyclization of PAH in sooting flames recently given by Frenklach and Warnatz. This qualitative mechanism offers a key to the understanding of the observed phenomenon, though a quantitative explanation, at the present state of analysis is lacking.