  We discuss the possibility of the asymmetry in $D^-/D^+$ production, from
$\pi^-$ beams, being a direct consequence of the properties of the light quark
fragmentation function into heavy mesons. The main features of the asymmetry,
as a function of $x_F$, are easily described. An integrated sum-rule for the
$D^-, D^+$ difference, is presented. Predictions for the asymmetry, in $B$
meson production, are given.
