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]
II.[Methods of Working][7]
I.[Discussion of Methods][7]
1.[Water cultures][7]
2.[Sand cultures][8]
3.[Soil cultures in pots][9]
4.[Field experiments][9]
II.[Details of Methods][10]
III.[Effect of Copper Compounds][15]
I.[Presence of Copper in Plants][15]
II.[Effect of Copper on the Growth of Higher Plants][17]
1.[Toxic effect][17]
(a)[Toxic action of copper compounds alone in water cultures][17]
(b)[Masking effect caused by addition of soluble substances to solutions of copper salts][20]
(c)[Effect of adding insoluble substances to solutions of copper salts][22]
(d)[Effect of copper on plant growth when present in soils][24]
(e)[Mode of action of copper on plants][25]
2.[Effect of copper on germination][27]
(a)[Seeds][27]
(b)[Spores and pollen grains][28]
3.[Does copper stimulate higher plants?][28]
4.[Action of copper on organs other than roots][30]
(a)[Effect of copper sprays on leaves][30]
(b)[Effect of solutions of copper salts on leaves][32]
III.[Effect of Copper on Certain of the Lower Plants][33]
[Conclusion][35]
IV.[Effect of Zinc Compounds][36]
I.[Presence of Zinc in Plants][36]
II.[Effect of Zinc on the Growth of Higher Plants][38]
1.[Toxic effect][38]
(a)[Toxic action of zinc salts alone in water cultures][38]
(b)[Effect of soluble zinc salts in the presence of nutrients][39]
(c)[Effect of zinc compounds on plant growth when they are present in soils][41]
(d)[Mode of action of zinc on plants][43]
2.[Effect of zinc compounds on germination][43]
3.[Stimulation induced by zinc compounds][45]
(a)[Stimulation in water cultures][45]
(b)[Stimulation in sand cultures][46]
(c)[Increased growth in soil][46]
4.[Direct action of zinc salts on leaves][47]
III.[Effect of Zinc on Certain of the Lower Plants][48]
[Conclusion][50]
V.[Effect of Arsenic Compounds][51]
I.[Presence of Arsenic in Plants][51]
II.[Effect of Arsenic on the Growth of Higher Plants][52]
1.[Toxic effect][52]
(a)[Toxic action of arsenic compounds in water cultures in the presence of nutrients][52]
(b)[Toxic effect of arsenic compounds in sand cultures][57]
(c)[Toxic effect of arsenic when applied to soil cultures][57]
(d)[Physiological considerations][59]
2.[Effect of arsenic compounds on germination][60]
3.[Do arsenic compounds stimulate higher plants?][61]
III.[Effect of Arsenic Compounds on Certain of the Lower Plants][62]
1.[Algae][62]
2.[Fungi][63]
[Conclusion][64]
VI.[Effect of Boron Compounds][65]
I.[Presence of Boron in Plants][65]
II.[Effect of Boron on the Growth of Higher Plants][67]
1.[Toxic effect][67]
(a)[Toxic action of boron compounds in water cultures][67]
(b)[Toxic action of boron compounds in sand cultures][70]
(c)[Toxic action of boron compounds in soil experiments][71]
2.[Effect of boron compounds on germination][72]
3.[Does boron stimulate higher plants?][73]
(a)[Water cultures][73]
(b)[Sand cultures][73]
(c)[Soil cultures][74]
III.[Effect of Boron Compounds on Certain of the Lower Plants][76]
[Conclusion][77]
VII.[Effect of Manganese Compounds][78]
I.[Presence of Manganese in Plants][78]
II.[Effect of Manganese on the Growth of Higher Plants][81]
1.[Toxic effect][81]
(a)[Toxic action of manganese compounds in the presence of soluble nutrients][81]
(b)[Toxic action of manganese compounds in sand cultures][82]
(c)[Toxic action of manganese compounds in soil cultures][82]
2.[Effect of manganese compounds on germination][84]
3.[Does manganese stimulate higher plants?][84]
(a)[Stimulation in water cultures][85]
(b)[Stimulation in soil cultures][86]
III.[Effect of Manganese Compounds on Certain of the Lower Plants][90]
IV.[Physiological Considerations of Manganese Stimulation][90]
[Conclusion][92]
VIII.[Conclusions][93]
[Bibliography][97]
[Index of Plant-Names][107]
[General Index][109]
[List of Illustrations][x]

LIST OF ILLUSTRATIONS

FIG.PAGE
1.[Sketch illustrating water culture methods][12]
2.[Photograph. Barley grown with copper sulphate]To face [20]
3.[Curve. Ditto][21]
4.[Photograph. Peas grown with copper sulphate]To face [29]
5.[Curve. Ditto][29]
6.[Curve. Barley grown with zinc sulphate][40]
7.[Photograph. Peas grown with zinc sulphate]To face [40]
8.[Curve. Ditto][41]
9.[Photograph. Barley grown with arsenious acid]To face [54]
10.[Curve. Ditto][55]
11.[Curve. Peas grown with arsenious acid][55]
12.[Curve. Barley grown with arsenic acid][56]
13.[Curve. Barley grown with sodium arsenite][56]
14.[Curve. Peas grown with sodium arsenite][57]
15.[Curve. Barley grown with boric acid][69]
16.[Photograph. Peas grown with boric acid]To face [69]
17.[Curve. Barley grown with manganese sulphate][85]
18.[Photograph. Ditto]To face [86]
19.[Photograph. Peas grown with manganese sulphate][86]