Relationship between dust and gas mass fraction as both a function of morphological type and environment – Virgo (top) and field (bottom). The dotted and dashed lines (they lie on top of each other and so are difficult to distinguish separately) correspond to a simple closed box chemical evolution model – Virgo dotted, field dashed line. The red line is the predicted maximum fractional dust mass for a dust-to-metals ratio of η = 0.5 and a stellar yield of p = 0.01.