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2. Wallace, T., "The Diagnosis of Mineral Deficiencies in Plants" (with Supplement) (London: H.M. Stationery Office, 1944).
3. Plant, W., Jones, J. O., and Nicholas, D. J. D., Ann. Rept. Long Ashton Research Station, 1944.
4. Bortner, C. E., Soil Sci., 30, 15 (1935).