Contents ix 



CHAP. PAGE 



(c) Toxic action of boron compounds in soil experi- 

 ments 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 cul- 



tures . ... . . . . . 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 . . ... . '"' . '". .' t . .' . 93 



BIBLIOGRAPHY .... . 97 



INDEX OF PLANT-NAMES . , . ....... . . 107 



GENERAL INDEX . 109 



LIST OF ILLUSTRATIONS 



