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 93 



BIBLIOGRAPHY 97 



INDEX OF PLANT-NAMES 107 



GENERAL INDEX . 109 



LIST OF ILLUSTRATIONS . 



