Clump bolometric luminosity vs. mass, as derived from the Hi-GAL observations. Symbols for starless and protostellar sources are as in Fig. 1. The dotted lines represent loci of constant 250μm flux density, ranging from 0.1 to 500 Jy, assuming a modified blackbody spectral energy distribution with β = 1.5 and a fixed distance of ~ 1 kpc. Roughly orthogonal to these are loci (dashed lines) at constant temperature, for the same modified blackbody. The green solid lines and small green filled circles represent the evolutionary tracks for the low- and high-mass regimes, respectively, taken from Molinari et al. (2008).