  We present a simple physical description of the off-diagonal gluon
distribution g (x,x^\prime,Q^2) and splitting function P_{gg}(x,x^\prime) which
enter the amplitude for diffractive vector meson production. We study the
off-diagonal effects both on the evolution in Q^2 and on the input
distribution. We predict the ratio $R$ of the off-diagonal to the diagonal
gluon density, x^\prime g(x,x^\prime,Q^2)/xg(x, Q^2), as a function of the
kinematic variables.
