Measurements were made on a beam‐plasma system under particularly simple and well‐defined conditions. The system could be operated at will in three distinct regimes, namely, (i) a quiescent steady‐state regime, (ii) a linear growth regime, and (iii) a nonlinear regime. The steady state is shown to agree with a static theory for a beam‐generated plasma. Measurements of spatially growing waves in the linear regime are described and compared with the theory discussed in Pt. I. Reasonable agreement is found when the effects of finite beam radius and collisions are taken into account, but it is indicated that the effect of radial inhomogeneity is also important. Some preliminary measurements on the nonlinear regime are reported and discussed in terms of the available nonlinear and quasilinear theories. The latter are judged too idealized to account for the nonlinear behavior of real beam‐plasma systems and suggestions are made concerning those respects in which they need generalizing.