  [Abridged] Norris et al. (1981) found that there was a distinct lack of
cyanogen-strong (CN-strong) stars in their sample of AGB stars, as compared to
their sample of RGB stars (which had roughly equal numbers of CN-normal and
CNstrong stars). Similar features have been discovered in the AGB populations
of other clusters. Unfortunately all of these studies suffer from low AGB star
counts so the conclusions are not necessarily robust -- larger, statistically
signifcant, sample sizes are needed.
  We outline the results of a literature search for relevant CN observations
and describe our observing proposal to test the suggestion that there are
substantial abundance differences between the AGB and RGB in galactic globular
clusters. The literature search revealed that the AGB star counts for all
studies (which are not, in general, studies about AGB stars in particular) are
low, usually being < or = 10. The search also revealed that the picture may not
be consistent between clusters. Although most clusters appear to have CN-weak
AGBs, at least two seem to have CN-strong AGBs (M5 & 47 Tuc). To further
complicate the picture, clusters often appear to have a combination of both
CN-strong and CN-weak stars on their AGBs -- although one population tends to
dominate. Again, all these assertions are however based on small sample
sizes.We aim to increase the sample sizes by an order of magnitude using
existing high quality photometry in which the AGB and RGB can be reliably
separated. For the observations we will use a wide-field, low- to
mid-resolution multi-object spectroscope. With the new information we hope to
ascertain whether significant abundance differences really exist.
