130 



Since the beginning of the work here reported, sever- 

 al papers have been published giving the results of 

 tests with toxins in soil cultures. 



Fraps (1) concludes from tests on a number of Texas 

 soils, that pyrogallol has no beneficial effects on plants 

 when used in connection with soil cultures. He also 

 studied the efiecl of vanillin, coumarin; and dihydroxy- 

 stearic acid when added to soils, and found little or no 

 injury to result therefrom. It was found that vanillin 

 and coumarin rapidly disappeared from the soils to 

 which they had been applied. 



Schreiner and Skinner (2) studied the toxic proper- 

 ties of salicylic aldehyde in soil, and found that even 

 small quantities were harmful to plants. Six months 

 iifter the application of salicylic aldehyde to field soils, 

 enough of the compound still persisted to cause injury 

 to growing plants. 



Skinner (8) has reported pot experiments in which 

 vanillin was added to three different soils on which 

 wheat was grown. His results show that on soils of 

 low fertility, vanillin was injurious; while on the fer- 

 tile Hagerstown soil, no harmfid effect resulted. In a 

 held lest at Arlington Farm, considerable injury to 

 ])lants was caused by comparatively small amounts of 

 vanillin; and the harmful effects of this compound 

 persisted for six months, as shown by i)lant tests, and 

 chemical examination of the soil for vanillin. 



Upson and Powell (4) used vanillin in connection 

 with soil cultures, and found little or no harmful effects 

 on wheat, even with concentrations up to 10(H) p. p. m. 

 of soil. The toxic effect of salcylic aklehyde was found 

 to be variable on different soils, but in all cases, the 

 injury was considerably less than in, solution cultures. 



By means of soil cultures in pots, Davidson (5) stud- 

 ied the toxicity of coumarin and vanillin, finding that 

 the germination of wheat was miimpau'ed, and the 

 growth retarded but little. He concludes that "On the 

 whole, it might be said that these experiments w^ould 

 liardly lend much support to the assumption that the 

 presence in the soil of organic substances toxic in 

 water cultures is a factor of considerable importance 

 under field conditions, when the other factors of plant 

 growth are normally good." 



(T) ^Fexas Station Bulleliii 174. 



(2) Bui. 108, U. S. Dc'pt. Agri. 



(3) Bui. 164, U. S. Dept .\gri. 



(4) .Jour. Ind. & Eng. Clicni. 7:.5. 



(5) .lour. Am. Soc. Agronomy, 7:.') 



