The size distribution, number concentration, and fraction charged of carbon particles at successive stage of formation in a low pressure flat flame were measured using molecular beam sampling, involving electrical beam deflection and electron microscopy of beam deposits and an optical absorption technique. Observed cluster-type structure within roughly spherical particles and decreasing particle number concentration following rapid nucleation, indicate the particles do indeed coagulate during growth. Particle size and number concentration data confirm this conclusion, although the experimental coagulation rate exceeds by a factor of about 10 the kinetic theory collision rate approximately adjusted for electrostatic forces, based upon the measured extent of particle charging, and Van der Waals attraction. Calculations, based upon extrapolation of the experimental coagulation rate constant into the flame region of significant particle nucleation and surface reaction, indicate that the particles nucleated first can grow predominantly by surface growth to a volume mean diameter of about 100 Å and that the number of primary particles per spherical unit within the final chainlike clusters is of order 10. Thus crystallites, the number of which is of order 103 per spherical unit, do not represent former particles.