1. Hewitt, E. J., A biological approach to the problems of soil acidity. Intern. Soc. Soil Sci. Trans. Dublin 1952,1, 107 (1953).
2. Hewitt, E. J., Sand and water culture methods used in the study of plant nutrition. Commonwealth Agr. Tech. Bur. Commun. No.22 (1952).
3. Holliday, R., Hodgson, D. R., and Townsend, W. N., Plant growth on ?Fly-Ash?. Nature (London)181, 1079 (1958).
4. Jones, L. H., The nature of power station ash and its effect on plant growth. Ph. D. Thesis, Birmingham University (1958).
5. McLean, F. T. and Gilbert, B. E., The relative aluminium tolerance of crop plants. Soil Sci.24, 163 (1927).