The occurrence of various visivle symptoms of foliar injury was assessed on a 5-point scale for each of the species. There was a distinct increase in the incidence of most types of injury in plant material which has been exposed to pH 2·5 acid fog. No clear pH-related trend in foliar injury occurred in plants exposed to acid fog at pH 3·5, pH 4·5 and pH 5·6, indicating that a threshold for a range of different types of visible injury may exist between pH 2·5 and pH 3·5 for all four species.
Bibliographical noteFunding Information:
The authors are grateful to Mr. C. R. Rafarel for setting up the misting unit, Mrs. S. A. Bell for maintaining treatments, Mr. C. P. Edge for graphics and Professor T. A. Mansfield for helpful discussion throughout the work. Financial support for MGB was provided by a NERC CASE studentship.