1. Allen, S. E., Grimshaw, H. M., Parkinson, J. A., and Quarmby, C.: 1974, Chemical Analysis of Ecological Materials, Oxford, Blackwell.
2. Asta, J. and Garrec, J. P.: 1980, Environ. Pollut. Ser. A. 21, 267.
3. Barbour, A. K., Castle, J. F., and Woods, S. E.: 1978, in A. Parker (ed.), Industrial Air Pollution Handbook, London, McGraw-Hill, p. 419.
4. Barkman, J. J.: 1969, in Air Pollution. Proceedings of the Wageningen Congress 1968, Wageningen, Centre for Agricultural Publishing and Documentation, p. 197.
5. Comeau, G. and LeBlanc, F.: 1972, Can. J. Bot. 50, 847.