Left: mean [N/C] ratio of the clusters analysed in this work (red diamonds) computed using only the member stars. The C and N abundances flagged as uncertain in Table 6 are not shown. The error bars depict the typical uncertainty in [N/C] propagated from the uncertainties in C and N listed in Table 7 and not the cluster scatter. Most clusters have good C and N abundances for one giant alone. A few selected results from the literature are included as blue symbols (Tautvaišien˙e et al. 2015, 2016; Drazdauskas et al. 2016a,b). Right: [N/C] ratio, in LTE, of selected Cepheids. References are given in Table 4. Two Cepheids suspected to be at the first crossing are shown as red stars; the other Cepheids are indicated as solid circles. The models of Lagarde et al. (2012), shown as black lines, extend only up to 6 M_⊙. The models of Ekström et al. (2012) are shown as blue lines and those from Bressan et al. (2012) as an orange line.