  Dynamics of an spatially limited electron beam in the inhomogeneous solar
corona plasma is considered in the framework of weak turbulence theory when the
temperature of the beam significantly exceeds that of surrounding plasma. The
numerical solution of kinetic equations manifests that generally the beam
accompanied by Langmuir waves propagates as a beam-plasma structure with a
decreasing velocity. Unlike the uniform plasma case the structure propagates
with the energy losses in the form of Langmuir waves. The results obtained are
compared with the results of observations of type III bursts. It is shown that
the deceleration of type III sources can be explained by the corona
inhomogeneity. The frequency drift rates of the type III sources are found in a
good agreement with the numerical results of beam dynamics.
