Transcriber's Note: Italic text is denoted by _underscores_ and bold text by ~tildes~. Superscripted text is enclosed in {braces} and preceded by a caret (^). CAMBRIDGE AGRICULTURAL MONOGRAPHS INORGANIC PLANT POISONS AND STIMULANTS CAMBRIDGE UNIVERSITY PRESS C. F. CLAY, MANAGER London: FETTER LANE, E.C. Edinburgh: 100 PRINCES STREET [Colophon] London: H. K. LEWIS, 136 GOWER STREET, W.C. London: WILLIAM WESLEY AND SON, 28 ESSEX STREET, STRAND New York: G. P. PUTNAM’S SONS Bombay and Calcutta: MACMILLAN AND CO., LTD. Toronto: J. M. DENT AND SONS, LTD. Tokyo: THE MARUZEN-KABUSHIKI-KAISHA _All rights reserved_ INORGANIC PLANT POISONS AND STIMULANTS BY WINIFRED E. BRENCHLEY, D.SC., F.L.S. Fellow of University College, London (Rothamsted Experimental Station) Cambridge: at the University Press 1914 Cambridge: PRINTED BY JOHN CLAY, M.A. AT THE UNIVERSITY PRESS PREFACE During the last century great and widespread changes have been made in agricultural practice--changes largely associated with the increase in the use of artificial fertilisers as supplements to the bulky organic manures which had hitherto been used. The value of certain chemical compounds as artificial manures is fully recognised, yet many attempts are being made to prove the value of other substances for the same purpose, with a view to increase in efficiency and decrease in cost. The interest in the matter is naturally great, and agriculturists, botanists and chemists have all approached the question from their different standpoints. In the following pages an attempt is made to correlate the work that has been done on a few inorganic substances which gave promise of proving useful in agricultural practice. Much of the evidence put forward by different workers is conflicting, and it is clear that no definite conclusions can yet be reached. Nevertheless, examination of the evidence justifies the hope that results of practical value will yet be obtained, and it is hoped that the analysis and coordination of the available data put forward in this book will aid in clearing the ground for those investigators who are following up the problem from both the academic and the practical standpoints. W. E. B. ROTHAMSTED. _October 1914._ CONTENTS CHAP. PAGE I. INTRODUCTION 1