IReprinted from The Biochemical Bulletin, 1912, i, pp. 413-427. March.] 



BIOCHEMICAL STUDIES ON SOILS SUBJECTED TO 



DRY HEAT 



FRED J. SEAVER and ERNEST D. CLARK 



(Laboratories of the New York Botanical Garden and of the Department of 

 Biological Chemistry of Columbia University) 



(With plate 7) 



INTRODUCTION 



In our earlier communications on the relation of heated soils to 

 the growth of plants we concerned ourselves only with the effects 

 on the fungi, especially Pyronema. In our first paper 1 we reported 

 that this fungus fails to develop on unheated soils, but can be made 

 to thrive and develop abundant fruit on soils that have been heated. 

 At that time it was suggested that heat seemed to produce chemical 

 changes in the soil as well as to eliminate the competition of bac- 

 teria, other fungi, etc., with Pyronema. In the second paper 2 our 

 experiments indicated that the inhibiting factor in unheated soils 

 did not seem to be a toxin destroyed by heat, as had been claimed by 

 Kasaroff. On the contrary, the better growth on soils which had 

 been heated in an oven appeared to be parallel to the amount of 

 soluble matter and to the depth of color of the water extract, both 

 of which in turn were dependent upon the temperature to which 

 the soils had been exposed. Temperatures of 125 to 180 C. gave 

 very dark-colored extracts, with the odor of burnt sugar, due to 

 the large amount of peculiar organic substances held in solution. 

 Extracts obtained from such heated soils proved to be ideal culture 

 media for Pyronema and others of the lower fungi, judging from 

 the difficulty we had in keeping the extracts sterile. The addition 

 of heated soil extracts to unheated soil did not render it favor- 

 able for Pyronema growth ; and furthermore, analysis showed that 



1 Seaver : Studies on pyrophilous fungi. I. The occurrence and cultivation 

 of Pyronema. Mycologia, 1 : 131-139. 1009. 



1 Seaver and Clark : Studies on pyrophilous fungi. II. Changes brought 

 about by the heating of soils and their relation to the growth of Pyronema and 

 other fungi. Mycologia, 2 : 100-124. 1910. 



413 



