It is demonstrated that an infinite set of string-tree level on-shell Wardidentities, which are valid to all sigma-model loop orders, can besystematically constructed without referring to the string field theory. Asexamples, bosonic massive scattering amplitudes are calculated explicitly up tothe second massive excited states. Ward identities satisfied by theseamplitudees are derived by using zero-norm states in the spetrum. Inparticular, the inter-particle Ward identity generated by the D2xD2' zero-normstate at the second massive level is demonstrated. The four physicalpropagating states of this mass level are then shown to form a large gaugemultiplet. This result justifies our previous consideration on higherinter-spin symmetry from the generalized worldsheet sigma-model point of view.
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