Tourmaline plashing ina noose of reeds, Lake Trasimene is being slowly strangled in ecology, no respecter of the Quattrocento. How could that sheeted opacity be looked at, after Arezzo, but as the filtered tint, wet lake-hue into fresco, Piero della Francesca laid like rain over sky, drapery, the roofs of houses? How, after Perugia, after the Louvre and the Uffizi, can the Umbria of Perugino be seen, five centuries later, except as he preempted it? -- as space turned inward, transparency set breathing to commend an attitude: Madonna, head dropping like a tulip, among donors. Fashions in felicity play hde and seek with decor; reigning apostolates shrink to a simper. It's the lake's look that breathes here, infinity's eutrophic emerald t hat won't keep either.