1. Spedding, D. J. Nature 224, 1229–1230 (1969).
2. Heck, W. W. & Brandt, C. S. in Air Pollution Vol. 2 (ed. Stern, A. C.) 158–229 (Academic, London, 1977).
3. Ashenden, T. W. & Mansfield, T. A. J. exp. Bot. 28, 729–735 (1977).
4. Bennett, J. H., Hill, A. C. & Gates, D. M. J. Air Pollut. Control Ass. 23, 957–962 (1973).
5. Unsworth, M. H., Biscoe, P. V. & Black, V. J. in Effects of Air Pollutants on Plants (ed. Mansfield, T. A.) 5–16 (Cambridge University Press, 1976).