  The role of parallel ion motion for zonal flow generation in
ion-temperature-gradient (ITG) mode turbulence is investigated with focus on
the effects of acoustic modes and toroidicity on the zonal flow. One possible
reason for the weak suppression of ITG turbulence by zonal flows found in
experiments in the Columbia Linear Machine (CLM) [Phys. Plasmas {\bf 13} 055905
(2006)] might be due to the small toroidicity ($\epsilon_n = 2L_n/R$) in the
experiment. The zonal flow is often directly dependent on the ITG mode and the
coupling of zonal flow to acoustic modes and hence is directly affected by any
change of the relevant parameters. The model consists of the continuity,
temperature and parallel ion momentum equations for the ITG turbulence. The
zonal flow time evolution is described by a Hasegawa-Mima like equation and a
fifth order zonal flow dispersion relation is derived. The results are
interpreted in terms of quality of zonal flows, i.e., the ratio of growth rate
and real frequency ($Q = \Omega^{IM}/\Omega^{RE}$). It is found that the
quality of the zonal flow rapidly decreases with decreasing toroidicity.
