  We study invariants of the adjoint action of the unipotent group in the
nilradical of a parabolic subalgebra of types Bn, Cn, Dn. We introduce the
notion of expanded base in the set of positive roots and construct an invariant
for every root of the expanded base. We prove that these invariants are
algebraically independent. We also give an estimate of the transcendence degree
of the field of invariants.
