CONTENTS 



OHAP. PACE 



I. Introduction 1 



II. Methods op 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 ov Copper CoMPoaNDS 15 



I. Presence of Copper in Plants 15 



II. Efiect 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 poUen 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 



