  Structure functions, as measured in lepton-nucleon scattering, have proven to
be very useful in studying the quark dynamics within the nucleon. However, it
is experimentally difficult to separately determine the longitudinal and
transverse structure functions, and consequently there are substantially less
data available for the longitudinal structure function in particular. Here we
present separated structure functions for hydrogen and deuterium at low
four--momentum transfer squared, Q^2< 1 GeV^2, and compare these with parton
distribution parameterizations and a k_T factorization approach. While
differences are found, the parameterizations generally agree with the data even
at the very low Q^2 scale of the data. The deuterium data show a smaller
longitudinal structure function, and smaller ratio of longitudinal to
transverse cross section R, than the proton. This suggests either an unexpected
difference in R for the proton and neutron or a suppression of the gluonic
distribution in nuclei.
