130 



prove conditions as can be noted from the table. There 

 can be no question regarding the persistence of vanillin 

 in this soil. It rose to the surface of the soil where it 

 was observed in crystals more than 40 days after its 

 addition to the pots. It is, therefore, believed that the 

 persistence of vanillin in the Arlington soil is due to 

 conditions in that soil which prevent the action of the 

 bacteria on the vanillin. 



What these conditions are can not be definitely 

 stated at the present stage of the investigation. The 

 soil, as was indicated above, is very acid. It was 

 found, however, that in an acid Alabama sandy loam, 

 having a lime requirement of 3400 pounds per acre, 

 vanillin, at the same concentration as was used in 

 the Arlington soil, was entirely destroyed in less than 

 57 days (6). 



Soil extracts of Alabama soil and Arlington soil to 

 which vanillin was added showed no difference in the 

 rate at which vanillin was destroyed by a pure culture 

 of a vanillin-destroying bacterium. 



It is possible that the persistence of vanillin in this 

 soil is due to poor oxygenation conditions. It has been 

 found that oxygen seems to influence the rate at which 

 vanillin is destroyed by a pure culture of a vanillin- 

 destroying bacterium and the destru-ction of vanillin 

 by this organism is an oxidative process, at least in its 

 early stage. The Arlington soil is a heavy silty clay 

 loam which compacts easily, probably excluding oxy- 

 gen to a large measure. 



Some condition which may be poor ox^'genation is 

 certainly unfavorable for bacterial growth in this soil. 

 This can be seen from the fact that, as is indicated in 

 Table 1 in the data for the check pots, the mere re- 

 moval, mixing and repotting caused a marked decrease 

 in the numbers of bacteria found 4 days later. This 

 decrease is perhaps best explained as a dilution effect. 

 If we assume that the upper layer of soil contained 

 numerous bacteria, while in the lower reaches of the 

 soil the bacteria which will develop on plates under 

 aerobic conditions were few or absent, then in mixing 

 the soil as was done at the time of treatment there 

 would be a decrease in the numbers because those bac- 

 teria in the upper layers were spread through the con- 

 tents of .the entire pot. Not only is this decrease evi- 

 dent 4 days later, but it continues to be evident for 

 something over 22 days as it is not until 30 days after 



