  We use the boundary state formalism for the bosonic string to calculate the
emission amplitude for closed string states from particular D-branes. We show
that the amplitudes obtained are exactly the same as those obtained from the
world-sheet sigma model calculation, and that the construction enforces the
requirement for integrated vertex operators, even in the off-shell case. Using
the expressions obtained for the boundary state we propose higher order terms
in the string loop expansion for the background considered.
