Clump mass versus clump radius for all the clumps. We divide the clumps into three groups, one group contains the clumps that belong to the spiral arm of the cloud (red crosses), and the other group contain the clouds that are outside the “spiral arm” (blue crosses). The third group contains clumps 2, 4 and 7, which exhibit clear evidences of ongoing star formation (red stars with numbers). IDs of the clumps are indicated. Lines of different free-fall time t_ff ~ ρ^{− 1/2} are included. The red solid line corresponds to the threshold of massive star formation M = 870 M_⊙(r/ pc)^1.33 derived in Kauffmann et al. (2010).