  We explore the effects of dissipationless merging on the Fundamental Plane of
elliptical galaxies by using a N-body code based on a new, high performance
numerical scheme (Dehnen 2002). We investigate the extreme cases of galaxy
growth by equal mass merging and accretion of small stellar systems; in a
subset of simulations we also consider the presence of dark matter halos around
the merging galaxies. Curiously, we found that the Fundamental Plane is
preserved by major merging, while in the accretion scenario its edge--on
thickness is only marginally reproduced, with substantial thickening in the
case of merging with low angular momentum. We also found that both the
Faber-Jackson and Kormendy relations are not reproduced by the simulations.
Finally, we discuss the implications of our results for the origin of the
Mbh-sigma and Magorrian relations. We found that dissipationless merging is
unable to reproduce the Mbh-sigma relation, if Mbhs add linearly (while the
Magorrian relation is nicely reproduced); on the contrary a black hole merging
with substantial emission of gravitational waves reproduces the Mbh-sigma
relation but fails at reproducing the Magorrian relation. [Abridged]
