  We observed a sample of 20 M giants with the Infrared Spectrograph on the
Spitzer Space Telescope. Most show absorption structure at 6.6-6.8 um which we
identify as water vapor, and in some cases, the absorption extends from 6.4 um
into the SiO band at 7.5 um. Variable stars show stronger H2O absorption. While
the strength of the SiO fundamental at 8 um increases monotonically from
spectral class K0 to K5, the dependence on spectral class weakens in the M
giants. As with previously studied samples, the M giants show considerable
scatter in SiO band strength within a given spectral class. All of the stars in
our sample also show OH band absorption, most noticeably in the 14-17 um
region. The OH bands behave much like the SiO bands, increasing in strength in
the K giants but showing weaker dependence on spectral class in the M giants,
and with considerable scatter. An examination of the photometric properties
reveals that the V-K color may be a better indicator of molecular band strength
than the spectral class. The transformation from Tycho colors to Johnson B-V
color is double-valued, and neither B-V nor BT-VT color increases monotonically
with spectral class in the M giants like they do in the K giants.
