(1978)
Volume
29
Part
6
Page from
319
Balea perversa has decreased greatly in areas that have suffered atmospheric pollution. When living on trees it is commonest on species with basic or neutral bark. Evidence is presented that in a polluted area it occurs only on those trees with the most base-rich bark. This could be due directly to reduction of the pH of the bark by SO2 from rainwater, to a secondary effect of that on the epiphytic flora, or to some combined effect.