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19. ROHRBAUGH, P. W. Mineral Nutrient Deficiencies in California Citrus Trees and their Causes California Citrograph, April-May, 1946
20. WHITE, CLARENCE Decorative Rock Mulches Organic Gardening, November, 1945—Emmaus, Pa.
21. RIOU, PAUL and DELORME, JOACHIM Manganese in Maple and Cane Sugars Comptes Rendues 200 1132-3 (1935) C.A. 294617
22. DELORME, JOACHIM Manganese in Maple and Cane Sugars Contrib. Lab. del'Ecole Hautes Etûdes Comm. Montreal No. 7, page 32 1937
23. BAUDISCH, OSKAR Biological Functions of Minor Elements Soil Sci. Vol. 60 No. 2 August, 1945
24. ELLIS, CARLETON; SWANEY, MILLER. W. Soilless Growth of Plants Reinhold Publishing Co. 1938
24. WILLIS, L. G. and PILAND, J. R. Minor Elements and Major Soil Problems Jour. Amer. Soc. Agronomy. 30—385—874 (1938)
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27. WISCHHUSEN, J. F. Recommendations for Feeding Manganese Manganese Research & Development Foundation, Cleveland 10, Ohio