Contents 



IX 



CHAP. PAOE 



(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? . V ~ . . 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 . . . . . . * . . 4 77 



VII. EFFECT OF MANGANESE COMPOUNDS . ... . . /. \ r . . . 78 



I. Presence of Manganese in Plants 78 



II. Effect of Manganese on the Growth of Higher Plants . 81 



1. Toxic effect . .. . . . .- . J ; --i 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 . , . . . . ' i . ' . 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 . . . :. :... j ; , . :. ; ^ ... 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 



