  We address the conjecture that at the tachyonic vacuum open strings get
transformed into closed strings. We show that it is possible in the context of
boundary string field theory to interpolate between the conventional open
string theory, characterized by having the D25 brane as the boundary state, and
an off-shell (open) string theory where the boundary state is identified with
the closed string vacuum, where holomorphic and antiholomorphic modes decouple
and where bulk vertex operator correlation functions are identical to those of
the closed string.
