Mass distribution dN / dMa) and dN / dlog (M) b) of the 60 starless (or Class 0) sources. The error bars represent the Poisson noise (in ). The vertical dotted line is the estimated 90% completeness limit. The thick solid line is the best power-law fit performed on the mass bins above the completeness limit. The best fit exponent, α and α_log, respectively, is given in the upper right corner of each panel. The IMF of single stars corrected for binaries (Kroupa 2001, K01) and the IMF of multiple systems (Chabrier 2005, C05) are shown in dashed (red) and dot-dashed (blue) lines, respectively. They are both vertically shifted to the same number at 5 M_⊙. The dotted (purple) curve is the typical mass spectrum of CO clumps (Blitz 1993; Kramer et al. 1998).