Toxicity, of nutrient salts, 1 of organic compounds, 4 of poisons, cause of, 22 of positive ions in copper compounds, 19, 22 reduction of, 39, 44 reduction of, by carbon black and ferric hydrate, 23 reduction of, by insoluble substances, 22 Toxin and nutrient, distinction between, 3 Transmission of power of resistance, 72 Valency, effect on toxicity, 44 Vanillin, 4 Variation in results on different substrata, 24 Zinc, absorption by roots, 42 carbonate, 38, 42, 43 effect of, on lower plants, 48 effect of, on plant and soil, 41 fixation of, 49 mode of action on plants, 43 oxide, 37, 47 oxide on leaves, deposition of, 47 storage in seeds, 43 sulphate, 38–49 sulphide, 42 CAMBRIDGE: PRINTED BY JOHN CLAY, M.A. AT THE UNIVERSITY PRESS. CAMBRIDGE AGRICULTURAL MONOGRAPHS GENERAL EDITORS: T. B. WOOD, M.A., Draper’s Professor of Agriculture in the University of Cambridge, and E. J. RUSSELL, D.Sc., Director of the Rothamsted Experimental Station, Harpenden, Herts. Each volume of this series will contain a summary of the present position on some particular aspect or branch of agricultural science by an expert of acknowledged authority. The treatment will be critical and impartial, and sufficiently detailed on all points of fundamental importance to be of use alike to all readers, but especially to those who are not in touch with an institution possessing a well equipped reference library. Full references will be given, and a bibliography attached for the benefit of those who wish to follow up any particular point. The following volumes are in preparation: ~The Strength of Wheat Flour.~ By Professor T. B. WOOD, M.A. ~The Constitution of the Soil.~ By E. J. RUSSELL, D.Sc. ~Disease Resistance.~ By R. H. BIFFEN, M.A., F.R.S., Professor of Agricultural Botany in the University of Cambridge. ~Poisonous Plants.~ By H. C. LONG. THE CAMBRIDGE FARM INSTITUTE SERIES GENERAL EDITORS: Professor T. B. WOOD, M.A., and E. J. RUSSELL, D.Sc. The volumes of this series are intended to meet the needs of the many Farm Institutes already in existence or about to be formed. They are intended for the average student whose object is to farm, rather than for the exceptional man who wishes to become an agricultural expert. Every endeavour will be made to attain a high standard educationally, by training students to take an intelligent interest in their daily work and to appreciate the beauty of the common objects among which their life will be passed. On the other hand the fact that farm students must earn their living on the land will not be lost sight of. The following will be among the first volumes: ~Farm Accounts.~ By C. S. ORWIN. [_Now ready_ ~Plant Life in Farm and Garden.~ By Professor R. H. BIFFEN, M.A.