The catalytic synthesis of various hollow carbon forms (carbon shells, hollow fibers, carbon nanotubes) has been performed on a supported nickel catalyst using carbon vapor as the precursor. Thin carbon films based on these forms have been obtained on silica substrates. It is concluded from the observed catalyst particle shapes and other experimental data that particles in liquid state are the active sites in the process of catalytic carbon nanotube growth. From this it is inferred that a vapor-liquid-solid (VLS) growth mechanism is operative in the catalytic process. The interfacial energy contribution to the total free energy of nanoparticles is assumed to be responsible for the significant depression in melting temperature of the catalyst particles. The variety of carbon forms is explained in terms of a periodic instability in the VLS-growth process.