  Plumes are one of the most ubiquitous features seen at the limb in polar
coronal holes and are considered to be a source of high density plasma streams
to the fast solar wind. We analyze STEREO observations of plumes and aim to
reinterpret and place observations with previous generations of EUV imagers
within a new context that was recently developed from Hinode observations. We
exploit the higher signal-to-noise, spatial and temporal resolution of the EUVI
telescopes over that of SOHO/EIT to study the temporal variation of polar
plumes in high detail. We employ recently developed insight from imaging (and
spectral) diagnostics of active region, plage, and quiet Sun plasmas to
identify the presence of apparent motions as high-speed upflows in magnetic
regions as opposed to previous interpretations of propagating waves. In almost
all polar plumes observed at the limb in these STEREO sequences, in all coronal
passbands, we observe high speed jets of plasma traveling along the structures
with a mean velocity of 135km/s at a range of temperatures from 0.5-1.5MK. The
jets have an apparent brightness enhancement of ~5% above that of the plumes
they travel on and repeat quasi-periodically, with repeat-times ranging from
five to twenty-five minutes. We also notice a very weak, fine scale, rapidly
evolving, but ubiquitous companion of the plumes that covers the entire coronal
hole limb. The observed jets are remarkably similar in intensity enhancement,
periodicity and velocity to those observed in other magnetic regions of the
solar atmosphere. They are multi-thermal in nature. We infer that the jets
observed on the plumes are a source of heated mass to the fast solar wind.
Further, based on the previous results that motivated this study, we suggest
that these jets originated in the upper chromosphere.
