  The effects of the orbital diffusion of stars and clusters on the galactic
abundance gradient have been modelled. For a single generation of field stars,
the results confirm previous analyses based upon the assumption of a linear
gradient with galactocentric distance. Though the dispersion in metallicity at
a given radius grows with time, the underlying slope across the disk remains
unchanged. For a disk dominated by a discontinuity in [Fe/H] beyond the solar
circle, but no gradient within the inner or outer disk, a gradient is derived
for any sample whose galactocentric baseline overlaps the discontinuity. The
consequence of orbital diffusion is to shift the observable edge of the
transition in [Fe/H] to smaller galactocentric distance. In contrast, star
clusters of a single generation evaporate so quickly that the small surviving
sample of the oldest clusters is statistically insufficient to define any but a
linear gradient. Inclusion of multiple generations of stars and clusters with a
plausible age-metallicity relation enhances these patterns by expanding the
metallicity range at a given galactocentric distance through the inclusion of
stars with a wide range in both age and galactocentric origin. For field stars,
the metallicity distribution of stars in the solar neighborhood is virtually
indistinguishable for the two cases modelled. Because ages, abundances, and
distances can be reliably determined for clusters and any sample of clusters is
invariably dominated by clusters formed over the last 2 Gyrs, the cluster
population offers a means for finding detailed structure within the recent
galactic abundance gradient. Using clusters to extend the galactocentric
baseline would supply an additional critical test of the discontinuity.
