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\def\etal{et~al.\ } Deep [O~III] $\lambda 5007$ of planetary nebulae (PN) in the bulge of M31 and in the Magellanic Clouds show that the faint end of the planetary nebulae luminosity function (PNLF) agrees extremely well with simple models based on uniformly expanding nebulae and non-evolving central stars. This behavior allows the total population of PN in a galaxy to be estimated by a simple extrapolation of the observed bright end of the PNLF\null. We use this property to compute the bolometric-luminosity specific PN densities ($\alpha_{2.5}$) of 25 early-type stellar populations, spanning a wide range in absolute magnitude, color, metallicity, and age. We show that there is a hard upper limit to $\alpha_{2.5}$ which is in perfect agreement with stellar evolution theory, but that the PN population of some galaxies is down by almost an order of magnitude. For bright galaxies, $\alpha_{2.5}$ correlates strongly with galaxy absolute magnitude, with large galaxies being PN deficient. PN density is also inversely correlated with the UV upturn seen in elliptical galaxies ($m_{1550}-V$), which suggests that the missing PN are becoming AGB manqu\'e objects. Significantly, the variations seen in $\alpha_{2.5}$ cannot be due solely to population age: in six galaxies with young or intermediate age stars, $\alpha_{2.5}$ varies by a factor of five. Instead, the evidence suggests that PN density depends on metallicity. This interpretation is supported by the existence of inverse correlation between $\alpha_{2.5}$ and Mg$_2$ index, the observed direct correlation between $\alpha_{2.5}$ and galactocentric distance in a synthetic galaxy formed from eight normal ellipticals, and the observed direct correlation between $\alpha_{2.5}$ and galactocentric distance in NGC~5128 (Hui \etal 1993). The sensitivity of $\alpha_{2.5}$ to stellar population suggests that by combining PNLF measurements with UV photometry and absorption line analyses, we can break the age-metallicity degeneracy for elliptical galaxies and produce realistic models for the population and chemical evolution of early-type systems.
