  Chemical and photometric models of elliptical galaxies with infall of
primordial gas, and subsequent ejection of processed material via galactic
winds, are described. Ensuring that these models are consistent with the
present-day colour-luminosity relation and the measured intracluster medium
(ICM) abundances, we demonstrate that the initial mass function (IMF) must be
significantly flatter (i.e., x<=0.80) than the canonical Salpeter slope (i.e.,
x=1.35). Such a ``top-heavy'' IMF is in agreement with the earlier conclusions
based upon closed-box models for elliptical galaxy evolution. On the other
hand, the top-heavy IMF, in conjunction with these semi-analytic infall models,
predicts an ICM gas mass which exceeds that observed by up to a factor three,
in contrast with the canonical closed-box models. Time and position-dependent
IMF formalisms may prove to be a fruitful avenue for future research, but those
presently available in the literature are shown to be inconsistent with several
important observational constraints.
