Plants contain very often inorganic elements in a form in which they cannot be utilized. It is therefore quite easy to mistake their presence either as a toxicity symptom or as a high requirement, when as a matter of fact these elements are present due to conditions unfavorable to metabolism, and they remained in bark and leaves as end products, in an inert form. Rather than being transmitted from soils to plant, their functions may consist of the formation of enzymes, proteins, hormones, chlorophyll, antibodies, vitamins, in carbon assimilation. When they have served such purposes they are not likely to be present in plants in anything like the amounts or forms as present in soils. They may come into question as catalysts or bio-catalysts, as sources of energy for microorganism, from which their optimum effects have been secured when they are not transmitted at all, causing changes, but remaining themselves unchanged. They are essential in the sense that the elements composing soils, sea, atmosphere are constantly energized, changed and used over and over again to create plant, animal and human life. In this cycle nothing is lost, only changed from old to new generations. Summary Soil factors for tree growth are physical, chemical and biological. To control the organisms of soils and plants is probably the most difficult problem in microbiology. It is not wise to alternate neglect with feverish attention when blights or other pests become epidemic or threatening. They may be of a nutritional, preventable rather than curable nature. Pathology and tree nutrition may as well become a constant part of your activities. References to the Literature 1. BEESON, K. C. The Mineral Composition of Crops U.S.D.A. Bulletin No. 369. March, 1941 2. FEARON, W. R. A Classification of the Biological Elements Sci. Proc. Royal Dublin Soc. Vol. 20 No. 35. February, 1933 3. WISCHHUSEN, J. F. Minerals in Agricultural and in Animal Husbandry Manganese Research & Development Foundation Cleveland 10, Ohio 4. RODALE, J. I. The Organic Forest--Editorial Organic Gardening, Emmaus, Pa. April, 1945, pp. 4-9 5. SCARSETH, GEORGE D. Growing Bananas on Acid SoilsAgriculture in the Americas, Vol. IV. October, 1944, No. 10 6. RAYNER, M. C. and NEILSON-JONES, W. Problems of Tree Nutrition Faber and Faber, Lt. London 7. ROACH, W. A. Soil Fertility and Trace Elements Soil Conservation, Washington. October, 1945 Condensed in Farmer's Digest, Ambler, Pa. January, 1946 8. CAMP, A. F. The Minor Elements in Citrus Fertilization Commercial Fertilizer, Atlanta, Ga. January, 1945 9. CHAPMAN, H. D.; BROWN, S. M.; and RAYNER, D. S. Nutrient Deficiencies in Citrus California Citrograph, May, 1945 10. McLEAN, F. T. Feeding Plants Manganese through the Stomata Science 66 (1927). Exp. Sta. Rec No. 58 11. SPRAY AND DUST SCHEDULES, Published Annually Florida Citrus Commission, Lakeland, Fla.