Seaver-Clark : Studies in Pyrophilous Fungi 113 



soil extract was also very characteristic, approaching that of the 

 heated-soil itself, while the unheated-soil extract had the odor of 

 ordinary moist earth. 



When concentrated by evaporation, the residue from the 

 heated-soil extract was of a dark brown color and possessed a 

 very strong odor of caramel. 



Other extracts of local soils were made with similar results. 

 When heated at low temperature the color of the soil extract 

 is often very pale, while the same soils when reheated at a higher 

 temperature yield a much more highly colored extract, which 

 indicates that high temperatures are necessary factors in produc- 

 ing a highly colored extract. 



The production of an extract from heated-soil of apparently 

 different composition from that obtained from unheated-soils 

 and which possessed the odor characteristic of soils most favor- 

 able to Pyronema growth, suggested the possibility that after all 

 we were dealing with a food problem, notwithstanding the fact 

 that this had apparently been disproved by Kasaroff. 



In order tO' test the effect of heat on other than local soils a 

 sample of North Dakota soil was obtained through the kindness 

 of Professor H. L. Bolley of the North Dakota Agricultural 

 College. A sample of this soil was heated and an extract 

 made as in previous experiments. The results were similar in 

 every way except that the extract was of a much darker color 

 (reddish-brown), a result which would naturally be expected by 

 reason of the large amount of organic material in the soil. A 

 more detailed account of the results of these tests will be given 

 in Section VII. 



Extracts of a Massachusetts soil sent by the kindness of Mr. 

 M. G. Clark did not differ materially from extracts of local New 

 York soils. 



We should call attention here to the correlation between the 

 temperatures necessary for the production of a strong or highly 

 colored extract and those necessary in order to render the soil 

 favorable to the growth of Pyronema. It has already been noted 

 in a previous paper that the higher the temperatures to which the 

 soils are heated (so far as our experiments had gone), the more 

 favorable are the conditions for the growth of the fungus. We 



