468 SOILS: PBOPEBTIES AND MANAQEMJENT 



ment with heat and volatile antiseptics. A number of 

 these theories will be mentioned, but it should be remem- 

 bered that much important work on the subject has been 

 done by investigators who have not advanced any hy- 

 potheses. 



387- Koch's theory. — Koch ^ was the first to offer 

 any explanation. In 1899 he stated it as his opinion that 

 carbon bisulfide has a directly stimulating action on the 

 plants themselves. He later ^ found ether to have a 

 similar action, and continued his experiments with carbon 

 bisulfide. He found that soil sterilized with heat pro- 

 duced better crops when treated with carbon bisulfide 

 than when not so treated, and concludes that the effect 

 of the antiseptic, therefore, cannot be due to the effect 

 of the antiseptic on bacteria. He also experimented with 

 field soils, and showed that the size of the crop on treated 

 soils is not proportional to the quantity of nitrogen 

 contained. 



The theory of Koch has been supported by Fred,^ who 

 fertilized soils with an abundant supply of sodium nitrate 

 and found that in every case in which carbon bisulfide 

 was added the growth and yield of crop were much su- 

 perior to those in the corresponding pots not treated with 

 that substance. He concludes that as there was no lack 

 of plant-food and other conditions favorable to plant 



1 Koeh, A. Untersueliungeii liber die Ursaciien der Rtiben- 

 mtidigkeit mit Besonderes Bertieksiehtigung der Sehwefel- 

 kohlenstoffbehandlung. Arb. Bent. Landw. GeselL, Heft 40, 

 Seite 7-38. 1899. 



2 Koob, A. XJeber die Wirkung von Aether Sehwefelkoh- 

 lenstoff auf Hobere und Niedere Pflanzen, Centrlb. f. Bakt., 

 II, Baud 31, Seite 175-185. 1911-1912. 



3 Fred, E. B. Effect of Fresh and Well-rotted Manure 

 on Plant Growth. Virginia Poly. Inst. Agr. Exp. Sta., Ann. 

 Kept. 1909-1910, pp. 142-159. 



