  Expressions for the P,T-violating NN potentials are derived for $\pi$, $\rho$
and $\omega$ exchange. The nuclear matrix elements for $\rho$ and $\omega$
exchange are shown to be greatly suppressed, so that, under the assumption of
comparable coupling constants, $\pi$ exchange would dominate by two orders of
magnitude. The ratio of P,T-violating to P-violating matrix elements is found
to remain approximately constant across the nuclear mass table, thus
establishing the proportionality between time-reversal-violation and
parity-violation matrix elements. The calculated values of this ratio suggest a
need to obtain an accuracy of order $ 5 \times 10^{-4}$ for the ratio of the
PT-violating to P-violating asymmetries in neutron transmission experiments in
order to improve on the present limits on the isovector pion coupling constant.
