Relative age parameter vs. absolute magnitude M_V for globular and old open clusters. Red filled symbols are GCs where the Na-O anti-correlation has been observed; open star symbols and open squares mark MW and Sagittarius GCs, respectively, for which not enough data are available; open circles are old open clusters (data from Lata et al. 2002). Finally, light blue crosses indicate several clusters that do not show evidence of Na-O anti-correlation: two GC members of Sagittarius dSph, one of the main body (Ter 7) and one of the stream (Pal 12); the new entry Rup 106; and two massive, old OCs, Be 39 and NGC 6791 (the latter indicated also in red, since its situation is still not completely assessed). Two orange, large circles indicate the other GCs of our project. Superimposed are lines of constant mass (light solid lines, see Bellazzini et al. 2008).