  We have proposed the plaquette-singlet solid (PSS) ground state for the
spin-1 antiferromagnetic Heisenberg two-leg ladder. Based on the PSS picture,
we discuss the correspondence of the PSS state to the valence-bond solid (VBS)
state of the ground state of spin-2 chain by introducing an appropriate
composite spin picture. When the bond alternation is introduced, there occur
quantum phase transitions and each phase can be identified with that in the
dimerized spin-2 chain. Furthermore, we argue that the VBS picture of spin-2S
chain can be applied to the ground state of spin-S two-leg ladder.
