Critical phenomena in high-energy lepton- and hadron-induced reactions

We argue that the nucleon seen in the Bjorken scaling region is a gas of quasi-free partons. As x decreases, for certain values of Q ² the partons in a nucleon coalesce to a liquid (saturation). Experimentally this phenomenon is manifested as the turn-over of the structure function derivatives. The phenomenon can be quantified in the framework of statistical models, percolation and other approaches to collective effects in the strongly interacting matter. Similarities and differences between the case of lepton-hadron, hadron-hadron and heavy-ion collisions are discussed.