LONGITUDINAL STRUCTURE FUNCTIONS

We show that nonuniversality effects associated with heavy flavor exci tations arise naturally when comparing longitudinal with transverse st ructure functions measured in muon and in neutrino induced reactions. Specifically, whereas in electromagnetic scattering of muons charm exc itation is dominated by the transverse cross section, the low Q2 neutr al and charged current neutrino scattering is predominantly given by t he longitudinal cross section. The A dependence induced on R by the di fferent Q2 dependence of the transverse and longitudinal shadowing is also discussed.