  We analyse recent data on the production of forward neutrons in deep
inelastic scattering at HERA in the framework of a perturbative QCD description
for semi-inclusive processes, which includes fracture functions. Using a model
estimate for the non-perturbative piece of the fragmentation process, in fairly
good agreement with the available data, we analyse the $Q^2$ dependence of the
resulting fracture functions, which is driven by non-homogeneous evolution
equations. We also propose a measurement of the pion production cross section
in the target fragmentation region as a new test of perturbative QCD, which in
this case predicts also a different $Q^2$ evolution with respect to the one
given by the usual Altarelli-Parisi equations.
