But there is a word of warning that may perhaps be issued to us as chemists, and conversely to biologists. Pliny two thousand years ago said, “The very signs also from which we form our judgment are often very deceptive”. We have already seen that there are often similarities in the symptoms exhibited by a given plant when it is suffering from a deficiency of one or another micro-nutrient. A combination of deficiencies may even be present, but the symptoms appear to be due to absence of one element only. But I have in mind something rather different from this: it is that fungus or virus diseases, or the reaction to an insect pest, may cause a plant to exhibit symptoms that suggest the presence of a nutritional deficiency. The final result so far as the plant is concerned may even be a deficiency, or at any rate a disturbance in the action, of some chemical element, but that upset is not the primary cause of the symptoms. Therefore I would suggest that when a diseased specimen indicates a previously unknown nutritional deficiency the chemist would be well-advised to call in the assistance of his colleagues, the plant pathologist and the entomologist, before finally deciding that the cause of the unsatisfactory condition of his specimen is primarily nutritional. It has been remarked that “without enzymes there can be no life”7 and also that “There exists a common, fundamental chemical ground-plan of composition to which all animals, and very probably other living organisms also, conform”.8 And again, quoting. “Nature knows only a few fundamental principles which she cleverly adapts to different purposes and circumstances”.9 The expectation, therefore, is that we shall find the same enzyme in both plants and animals. A classification of enzymes, with their accompanying metals, has been given by Seekles, as follows (modified)10 (1)Synthests and destruction of tissue elements (mainly Poten) A. d-Pepttidases: Mn. Co. Fe, Zn, Mg. B. Argrnase — Mn. Co. N1. Ca. V. C. iso — Citric acid dehydrogenase: Mn, Mg. (2) Energy Change (oxrdation - reduction) A Haemoglobin: Fe Haemocyann: Cu Raspiratory: Enzy me Fe Cytochromes: Fe. Mn. Peroxydase: Fe. Mn. Transferen of Oxygen Catalase: Fe Oxidases: Cu B. Phosphate tiansfen: Mg, Mn. C. Enolase: Mg, Mn, Zn D. Catboxylase: Mg. Mn. Zn E. Pyruvne acid dehydhogeans: Mg. Zn F. Phosphases (vanous): Mg G. Zymase (yeast): Mn H. Carbonic acid anhydrase: Zn J. Phodphohpoid oxidation: V. K. Lipases: Ca. Mn. (3) Detixucatuib reathons A. Tyrosinase: Cu B. Polyphenoloxydases: Cu C. Diamno-oxydase: Co (4) Transference of nervous stimult A Chlinesterase: Mn, Mg, Ca, Ba.