[en] Complex structures of carbon nanotubes formed from a conventional carbon arc-discharge method have been revealed by high-resolution transmission electron microscopy (HRTEM). The branching and the droplet growth phenomena observed by HRTEM indicate that the formation and growth of carbon nanotubes from an arc-discharge method cannot be simply processed from one end to another. Based on the observation of the growth phenomena and the amorphous carbon residue inside the hollow core of carbon nanotubes, a two-step growth model of carbon nanotubes has been proposed