  We have investigated the structural and dynamical properties of triaxial
stellar systems whose surface brightness profiles follow the r^{1/n} luminosity
law - extending the analysis of Ciotti (1991) who explored the properties of
spherical r^{1/n} systems. A new `analytical' expression that accurately
reproduces the spatial (i.e. deprojected) luminosity density profiles (error <
0.1%) is presented for detailed modelling of the Sersic family of luminosity
profiles. We evaluate both the symmetric and the non--axisymmetric components
of the gravitational potential and force, and compute the torques as a function
of position. For a given triaxiality, stellar systems with smaller values of n
have a greater non-axisymmetric gravitational field component. We also explore
the strength of the non-axisymmetric forces produced by bulges with differing n
and triaxiality on systems having a range of bulge-to-disc ratios. The
increasing disc-to-bulge ratio with increasing galaxy type (decreasing n) is
found to heavily reduce the amplitude of the non-axisymmetric terms, and
therefore reduce the possibility that triaxial bulges in late-type systems may
be the mechanism or perturbation for nonsymmetric structures in the disc. Using
seeing-convolved r^{1/n}-bulge plus exponential-disc fits to the K-band data
from a sample of 80 nearby disc galaxies, we probe the relations between galaxy
type, Sersic index n and the bulge-to-disc luminosity ratio. These relations
are shown to be primarily a consequence of the relation between n and the total
bulge luminosity. In the K-band, the trend of decreasing bulge-to-disc
luminosity ratio along the spiral Hubble sequence is predominantly, although
not entirely, a consequence of the change in the total bulge luminosity; the
trend between the total disc luminosity and Hubble type is much weaker.
