It is confirmed that geodesic string junctions are necessary to descri
be the gauge vectors of symmetry groups that arise in the context of I
IB superstrings compactified in the presence of nonlocal 7-branes. By
examining the moduli space of 7-brane backgrounds for which the dilato
n and axion fields are constant, we are able to describe explicitly an
d geometrically how open string geodesics can fail to be smooth, and h
ow geodesic string junctions then become the relevant BPS representati
ves of the gauge bosons. The mechanisms that guarantee the existence a
nd uniqueness of the BPS representative of any gauge vector are also s
hown to generalize to the case where the dilaton and axion fields are
not constant. (C) 1998 Elsevier Science B.V.