Abstract. Let E be a Riesz space and let E ∼ denote its order dual. The orthomorphisms Orth(E) on E, and the ideal center Z(E) of E, are naturally embedded in Orth(E ∼ ) and Z(E ∼ ) respectively. We construct two unital algebra and order continuous Riesz homomorphismsandthat extend the above mentioned natural inclusions respectively. Then, the range of γ is an order ideal in Orth(E ∼ ) if and only if m is surjective. Furthermore, m is surjective if and only if E has a topologically full center. (That is, the σ(E, E ∼ )-closure of Z(E)x contains the order ideal generated by x for each x ∈ E+.) As a consequence, E has a topologically full center Z(E) if and only if Z(E ∼ ) = π · Z(E) ′′ for some idempotent π ∈ Z(E)′′ .