  Primary energy spectrum of cosmic rays exhibits a knee at about $3$ PeV where
a change in the spectral index occurs. Despite many efforts the origin of such
a feature of the spectrum is not satisfactorily solved yet. Here it is proposed
that the steepening of the spectrum beyond the knee may be a consequence of
mass distribution of progenitor of cosmic ray source. The proposed speculative
model can account all the major observed features about cosmic rays without
invoking any fine tuning to match flux or spectra at any energy point. The
prediction of the proposed model regarding primary composition scenario beyond
the knee is quite different from most of the prevailing models of the knee and
thereby can be discriminated from precise experimental measurement of the
primary composition.
