Chapter I: 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

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