  We study the conductance threshold of clean nearly straight quantum wires in
the magnetic field. As a quantitative example we solve exactly the scattering
problem for two-electrons in a wire with planar geometry and a weak bulge. From
the scattering matrix we determine conductance via the Landauer-Buettiker
formalism. The conductance anomalies found near 0.25(2e^2/h) and 0.75(2e^2/h)
are related to a singlet resonance and a triplet resonance, respectively, and
survive to temperatures of a few degrees. With increasing in-plane magnetic
field the conductance exhibits a plateau at e^2/h, consistent with recent
experiments.
