  We analyze the effect of an auxiliary scatterer, such as the potential of a
scanning tip, on the conductance of an interacting one-dimensional electron
system. We find that the differential conductance for tunneling into the end of
a semi-infinite quantum wire reflects the separation of the elementary
excitations into spin and charge modes. The separation is revealed as a
specific pattern in the dependence of the conductance on bias and on the
position of the scatterer.
