phenoaanon, that w©«d» injure crops. Two of these causes, 

 however, in the opinions of experimentalifita etftad pre- 

 emiaeat j naaely, injuries due to lose of soil moisture, 

 and to loss of plant food. The chief attention was, ther* " 

 fore, directed to the'^e cause-a. 



The thesis is divided as follows : 

 1. Historical 

 S. Experimental 

 3. Appendix. 



In the historical part, the literature is reviewed 

 and discussed. • 



In the experimental part, an account of the 

 experiment is given, together with discussions chiefly 

 in the light of the historical treatment. 



In the Appendix, a limited study of the soil under 

 experiment is made. 



