The heavy metals, copper, zinc, manganese, iron and molybdenum are now accepted as essential plant nutrients, and their probable significance as key factors in enzyme systems has suggested that they may directly or indirectly influcncp vitamin synthesis.The development of technical reliability in the determination of ascorbic aeid in plant material, Lugg (1942) and in the location of micronutrient and potash deficiency by the response of herbage legumes in controlled soil cultures, Ferrns and Trumble (1943), made possible the work herein described.The literature concerning variation of ascorbic acid content with applications of mieronutrients has been reviewed by Maynard and Beeson (1943), who found it too contradictory to give any definite conclusion. They quoted two instances of increase in ascorbic acid with zinc in oranges, Roy and Bahrt (1940) and Cowart (1941), but cited evidence brought forward by Lyon, Beoson and Ellis (1943) which showed that marked increases in the growth of tomatoes following the addition of zinc were unaccompanied by any change in the concentration of ascorbic acid.Hester and Kohman (1940) and Rugawara (1941) secured an increase in ascorbic acid with the application of potash to tomatoes and potatoes respectively. Hamner, Lyon and Hamner (1942) on the other liand, found no substantial effect of potash on tomatoes when other elements were kept sufficiently high.Rudra (1944) has reported that "manganese has a specific role in the synthesis of ascorbic acid by plants and animals", and Hester (1941) has found a lower level in tomato jjUints untreated with manganese than those to which manganese was added. On the other hand Lyon aud and Lyon, Beeson and Ellia (1943), obtained no change in the concentration of ascorbic acid with the addition of this element.There is considerable evidence to indicate that climatic factors affect the vitamin content of plants grown for food; in particular the dominant rolo of light in the ascorbic acid content of plants has been recognized, Maynard and Be«son (1943). Work by B«id (1942) indicated that both high light intensity and long days were conducive to higher ascorbic acid values in cow peas; a sufficient supply of available ma,ior nutrients, with special reference to nitrogen, was stated to favour a higher content of ascorbic acid, provided light was available for the active synthesis of carbohydrate.While it is well known that the ascorbic aeid content of plants varies with the locality, it has been generally impossible to ascertain the specific factors involved iu the environmental complex. In all cases there has been insufficient <'ontrol of the individual variables concerned. No work appears to have been carried out on the possible interactions of micronutrients and climatic factors as affecting the ascorbic acid content.Recently Hamner (1945), in a further review, concluded that variations in the ascorbic acid content of plants are so influenced by varietal differences and by climatic conditions that soil factors and tho application of ferti...