Observational constraints on the chemical evolution of Galactic CNO abundances: abundance ratios log (C/O) and log (N/O) vs. O abundance. Left panels: black triangles: early B-stars from the literature extracted from Fig. 12. Data for low-mass stars are displayed as grey symbols (green in the online edition) – squares: Gustafsson et al. (1999, solar-type dwarfs); crosses: Fabbian et al. (2009, solar-type dwarfs and subgiants); diamonds: Spite et al. (2005, unmixed cool giants); plus signs: Israelian et al. (2004, unevolved solar-type stars). Solar abundance ratios of Asplund et al. (2009) are also indicated ( ⊙ ). Right panels: black dots: unmixed objects from the present work, black circles: unmixed stars from NS11. Data from the literature like in the left panels. The CAS is also indicated (red star). Error bars (statistical 1σ-uncertainties) typical for individual stars in the present study are shown.