  We extend the recently established Mellin correspondence of supergravity and
superstring amplitudes to the case of arbitrary helicity configurations. The
amplitudes are discussed in the framework of Grassmannian varieties. We
generalize Hodges' determinant to a function of two sets of independent
coordinates and show that tree-level supergravity amplitudes can be obtained by
contour integrations of both sets in separate Grassmannians while in
superstring theory, one set of coordinates is identified with string vertex
positions at the disk boundary and Mellin transformed into generalized
hypergeometric functions of Mandelstam invariants.
