The description of F 2 at low Q 2

We analyse the data for the proton structure function F 2 over the entire Q 2 domain, including especially low Q 2 , in terms of perturbative and non-perturbative QCD contributions. The small distance configurations are given by perturbative QCD, while the large distance contributions are given by the vector dominance model and, for the higher mass qq states, by the additive quark approach. The interference between states of different q ¯ q mass (in the perturbative contribution) is found to play a crucial role in obtaining an excellent description of the data throughout the whole Q 2 region, including photoproduc-tion.