  The existence two S-dual descriptions of (N,1) string bound states suggests
that the strong coupling behaviour of electric flux lines in large N 2D SYM
theory has a dual description in terms of weakly coupled IIB string theory. In
support of this identification, we propose a dual interpretation of the SYM
loop equation as a perturbative string Ward identity, expressing the conformal
invariance of the corresponding boundary interaction. This correspondence can
be viewed as a weak coupling check of the matrix string conjecture.
