  We further the recent discussion on the relation between the star-formation
rate (SFR) of a galaxy and the luminosity of its brightest star-cluster (SFR
vs. M$_{V}^{brightest}$). We first show that the observed trend between SFR vs.
M$_{V}^{brightest}$ is due to the brightest cluster in a galaxy being
preferentially young (<15 Myr - for a constant SFR) and hence a good tracer of
the current SFR, although we give notable exceptions to this rule. Using a
series of Monte Carlo simulations we show that a pure power-law mass function
with index, alpha=2, is ruled out by the current data. Instead we find that a
Schechter function (i.e. a power-law with an exponential truncation at the high
mass end) provides an excellent fit to the data. Additionally, these
simulations show that bound cluster formation (in Msun/yr) represents only
~8+-3% of the total star-formation within a galaxy, independent of the
star-formation rate. From this we conclude that there is only a single mode of
cluster formation which operates over at least six orders of magnitude in the
SFR. Using this relation, we can extrapolate backwards in time in order to
estimate the peak SFR of major merger galaxies, such as NGC7252, NGC1316 and
NGC3610. The derived SFRs for these galaxies are between a few hundred and a
few thousand solar masses per year. The inferred far infrared luminosity of the
galaxies, from the extrapolated SFR, places them well within the range of
Ultra-luminous galaxies (ULIRGs) and for NGC 7252 within the Hyper-luminous
infrared galaxy regime. Thus, we provide evidence that these post merger
galaxies passed through a ULIRG/HLIRG phase and are now evolving passively.
Using the current and extrapolated past SFR of NGC 34, we infer that the ULIRG
phase of this galaxy has lasted for at least 150 Myr.
