  Disk amplitudes of tachyons in two-dimensional open string theories
(two-dimensional quantum gravity coupled to $c \leq 1$ conformal field
theories) are obtained using the continuum Liouville field approach. The
structure of momentum singularities is different from that of sphere amplitudes
and is more complicated. It can be understood by factorizations of the
amplitudes with the tachyon and the discrete states as intermediate states.
