Na–O anti-correlation in NGC 5897 (solid circles) on the data for Galactic GCs of Carretta et al. (2009b,c; gray points). The Na abundances have been corrected for NLTE, with typical corrections on the order of −0.05 dex. The dashed lines are empirical separations into primordial (lower part), intermediate (middle), and extreme (upper left corner) populations. Shown as a solid red line is the best-fit simple dilution model for NGC 5897, compared to the curve of the metal-poor GC M 15 from Carretta et al. (2009c; dashed red line).