[en] Assuming scaling in the longitudinal reduced momentum in the overall center of mass for the parton fragmentation function, there are, in any hard scattering model, at least three possible sources of a lack of scaling in (1/σ) (dσ/dxsub(e)). In this paper these causes are analysed particularly one of them, 'the skew mechanism', which occurs because the axes of the partons are not the x-axis used to express the reduced momenta of the hadrons and because, simultaneously, the transverse momentum of hadrons inside partons is not negligible. A particular result of this study is that the lack of scaling in (1/σ)(dσ/dxsub(e)) observed by C.C.H.K. and B.F.S. collaborations is not necessarily in contradiction with the scaling in the longitudinal reduced momentum of the jet. (author)