  Bushes of normal modes represent the exact excitations in nonlinear physical
systems with discrete symmetries [Physica D117 (1998) 43]. The present paper is
the continuation of our previous paper [Physica D166 (2002) 208], where these
dynamical objects of a new type were discussed for the monoatomic nonlinear
chains. Here, we develop a simple crystallographic method for finding bushes in
nonlinear chains and investigate stability of one-dimensional and
two-dimensional vibrational bushes for both FPU-alpha and FPU-beta models, in
particular, of those revealed recently in [Physica D175 (2003) 31].
