We re-investigate the problem of electron beam propagation and the formation of type III bursts, assuming that the corona is inhomogeneous and the magnetic field is split in small independent fibers. We start by injecting in each fiber a beam with random characteristics (beam density, beam energy, etc.) and follow its non linear evolution during propagation. We add the contribution of N independent beams in each frequency and form the expected spectrum. We discuss the fine structure of type III bursts, the decimetric spikes associated with type III bursts and the formation of groups of type III bursts.
keywords : sun: Type III solar radio bursts-- electron beams-- flares--sun:beams--sun:radio bursts.