  We establish the model-independent spin structure of the matrix elements for
the near-threshold scalar meson production in $pp-$ and $np$-collisions, when
the final particles are emitted in S-state. Polarization phenomena are derived
in a general form. The properties of the $t-$channel dynamics, which is based
on different meson exchanges, are studied in terms of the $s-$channel
parametrization of the matrix element. The prediction of a 'realistic' model,
based on $\pi+\sigma$-exchanges are also presented.
