Microscopic in situ observations.and a posteriori surface topography by means of optical and scanning electron microscopy have been carried out in order to study the growth of large-grain polycrystalline silicon films from the gas phase onto a graphite substrate coated with a liquid layer of tin or aluminum. In the present study, only the initial stages of the process, where crystal growth is governed by vapor-liquid-solid mechanisms, are considered. For the growth of the crystallites in the polycrystalline layers, which occur in two morphological forms, viz., needles and platelets, two different mechanisms could be identified: (i) a twin plane reentrant edge (TPRE) mechanism, leading to a fast lengthwise growth of needles and a fast sidewise growth of platelets; and (ii) a nucleation mechanism, accounting for a slow thickness growth of the needles and a slow expansion of the platelike crystals. On the upper surfaces of some needles and platelets a capricious surface pattern (always in conjunction with the occurrence of some solidified metal droplets) could be identified, which could be interpreted in terms of a two-dimensional VLS growth mechanism.