ORGANIC CONSTITUENTS OF THE SOIL SOLUTION 8l 



the soils cited but with samples from adjacent good and poor 

 spots in fields on several soil types from widely separated areas ; 

 for instance, Cecil clay from near Statesville, North Carolina; 

 Sassafras loam from Maryland; Windsor sand from Delaware; 

 and similar results were obtained. In other words, these water 

 cultures produced plants which showed much the same differ- 

 ences, in kind and degree, as had been observed in the field. 

 This was recognized as an important step forward, for it indi- 

 cated that whatever was making a difference in the crop-produc- 

 ing power of these soils in the field was transmitted to their 

 aqueous extracts, and methods for studying the chemical prop- 

 erties of solutions are far in advance of methods for studying 

 mixtures of solids. 



The soil extracts described above were subjected to a careful 

 analysis for their mineral constituents. They were found to be 

 practically identical in this respect. Further, the poor extract 

 contained decidedly more nitrates than the good from three 

 to four times as much. It follows, therefore, that the difference 

 in the soils which produced a good and a poor crop respectively, 

 was not due to a difference in mineral plant nutrients, or other 

 mineral differences probably, nor to their respective content of 

 nitrates. Consequently, the poor solution was such, not because 

 of the lack of anything, but because of the presence of some- 

 thing inimical or "toxic" to plant growth; and further, this 

 something must be an organic substance or substances more or 

 less soluble in water. This conclusion was confirmed in the 

 following way. 



Samples of the poor solution from the soil obtained near 

 Statesville, N. C., were diluted twice, five times, and ten times, 

 and wheat seedlings were grown in these solutions, using a sam- 

 ple of the good solution as a check. It was found after several 

 days growth that the plants in the solution diluted tenfold were 

 about as good, or perhaps slightly better, than those grown in 

 the check solution. In every case diluting the poor solution 

 had improved it for plant growth, and the higher the dilution 

 the greater the improvement, in spite of the consequent dilution 

 of the mineral plant nutrients. The only explanation of these 



