  We analyze new measurements of the Mg_2 central line strength index and
velocity dispersion (sigma) for the galaxies of the ENEAR survey. The
observations are now complete (da Costa et al. 2000) and the sample contains
1223 early-type galaxies. We also analyze the line strength indices for a
sample of 95 spiral bulges (from Sa to Sbc). For the early-type galaxies we
find: i) that the Mg_2-sigma relation for Es and S0s are nearly the same, with
both populations showing comparable scatter, and ii) a marginal difference in
the slope of the Mg_2-sigma relation for cluster and field early-type galaxies.
However, we suggest that before interpreting such a difference in the framework
of a mass-metallicity relation, it is important to take into account the
effects of rotation in the Mg_2-sigma relation. Our preliminary results
indicate that once the rotation effects are minimized by choosing a sample
containing only slow rotators, the Mg_2-sigma relation is similar both for
isolated and clustered galaxies. More data on rotational velocities of
early-type galaxies are needed to confirm this result. For spiral bulges, we
find that their locus in the Mg_2-sigma plane lies always below the one
occupied by early-type galaxies.
