294 THE FARMER OF TO-MORROW 



dihydroxystearic acid entirely. Here, then, is 

 a use of chemical fertilizers not explained by 

 the "plant food" theory. 



On the other hand, there are other sub- 

 stances found in normal soils which are ren- 

 dered even more toxic by the addition of 

 nitrates. These substances are, for the most 

 part, nitrogenous themselves. As an instance, 

 a substance called cumarin is found to have a 

 very characteristic effect on plants, stunting 

 the growth and distorting the leaves. The 

 addition of nitrogen or potash does not affect 

 it at all. Yet the addition of even a minute 

 quantity of a phosphate salt clears the soil of 

 this toxin and a healthy plant is produced. 

 Potash salts affect still another series of toxic 

 substances. 



In presenting in detail the history of his 

 investigations of this phase of soil fertility be- 

 fore the American Association for the Ad- 

 vancement of Science, at a recent Washing- 

 ton meeting, Doctor Oswald Schreiner was 

 led to remark: 



"These actions of the different fertilizer 

 combinations, or different fertilizer require- 

 ments, as they may be styled, show a certain 

 parallelism with field observations on soils and 



