  We show how a difference in the correlation length longitudinally and
transversely, with respect to the jet axis in e+e- annihilation, arises
naturally in a model for Bose-Einstein correlations based on the Lund string
model. In genuine three-particle correlations the difference is even more
apparent and they provide therefore a good probe for the longitudinal
stretching of the string field. The correlation length between pion pairs is
found to be rather independent of the pion multiplicity and the kaon content of
the final state.
