  It has been argued in previous papers that an ion-proton plasma is formed at
the polar caps of neutron stars with positive polar-cap corotational charge
density. The present paper does not offer a theory of the development of
turbulence from the unstable Langmuir modes that grow in the outward
accelerated plasma, but attempts to describe in qualitative terms the factors
relevant to the emission of polarized radiation at frequencies below 1 - 10
GHz. The work of Karastergiou and Johnston is of particular importance in this
respect because it demonstrates in high-resolution measurements of the profiles
of 17 pulsars that the relative phase retardation between the O- and E-modes of
the plasma is no greater than of the order of pi. Provided the source of the
radiation is at low altitudes, as favoured by recent observations, this order
of retardation is possible only for a plasma of baryonic-mass particles.
