Space-time evolution and transverse- momentum structure of jets

We discuss models in which the temporal evolution of hadronic jets and the rapidity ordering of particles within jets are correlated. Observable effects on the particle average transverse momentum (energy and longitudinal momentum dependence) characteristic of such models are pointed out. In particular, models in which, within jets, slow particles are produced first and fast particles come out last should exhibit the well-known seagull effect, with 〈p_T〉 rising, for fixed x, proportionately to the square root of the mean particle multiplicity. If, by analogy, the transverse-momentum distributions of partons also exhibit such features, then we have a source of scaling violation in deep inelastic reactions that shows up at high energies rather than at low energies, and a source for an energy and Q² dependent 〈q_T〉 in lepton pair production.