i 9 i2] Fred J. Seaver and Ernest D. Clark 4 J 5 



a bulletin on the effects of steam sterilization, studying the chemical 

 and agricultural phases rather than the bacteriological ones. Their 

 soils were steamed for various periods of time in an autoclave under 

 a pressure of two atmospheres. The water-soluble matter was 

 greatly increased by this treatment, but upon standing untouched 

 the soils gradually went back to their original state, at least as far 

 as their soluble matter was concerned. These authors found that 

 both ammonification and nitrification were absent for three months 

 after heating. The extracts of these steamed soils were distinctly 

 unfavorable to the growth of seedlings, but upon proper dilution the 

 seedlings made a better growth than in extracts of unsteamed soils. 

 They speak of the "injurious" results of steaming, but, of course, 

 this term applies only when judged from the standpoint of the green 

 plant. The lower fungi like Pyronema flourish on these extracts 

 which are toxic to the seedlings of the higher plants. After stand- 

 ing three months the steamed soils made an excellent showing when 

 planted with wheat. The fact that ammonification is at a standstill, 

 and that such steamed soils are harmful to green plants immediately 

 after this treatment, is probably attributable to the same cause, 

 namely, the complete destruction of beneficial bacteria by the higher 

 temperatures they employed. Russell and Hutchinson did not find 

 this to be the case, probably because the temperature they used was 

 sufficient to kill protozoa but not the spores of bacteria. This varia- 

 tion in temperature might well account for the differences in the 

 results of these two groups of investigators. However, it is doubt- 

 ful if it is correct to speak of the sterilization of a soil, since, as 

 pointed out to us by Dr. Schreiner of the Bureau of Soils, it is 

 impossible to say that the heat has entered the interior of the soil 

 mass sufficiently to kill every living organism and spore. Fletcher 5 

 does not believe that the advantage of heating soils comes from 

 changing the bacterial flora or increasing the soluble matter. He 

 feels that the heat destroys some toxin present in the unheated soil. 

 He heated soils to 95 ° and 170 C. and found that afterwards corn 

 made a better growth upon both the heated soils than upon the 

 unheated control. The work of other investigators and also our 

 own does not agree with Fletcher's conclusion that soils heated to 



5 Fletcher : Effect of previous heating of the soil on the growth of plants 

 and the germination of seeds. Cairo Science Jour., 4: 81-6. 1911. 



