118 



Mycologia 



inoculated both liquids with the spores of Pyronema. In a week, 

 the flask containing the dark-colored distillation residue was filled 

 with the mycelium, while the other flask also had a considerable 

 growth of Pyronema, the latter flask and liquid being perfectly 

 transparent, with the silvery clumps of mycelium resting on the 

 bottom of the flask {pi. 25, f. i). Thus it seemed that distillation 

 did not cause any appreciable separation of the substances in the 

 extract, i. e., judging from its effect on the growth of Pyronema. 



VIL Chemical Studies of Soil Extracts 

 (a) Quantitative 

 As already noted, the color, odor, and general appearance of 

 heated-soil extracts indicate that the composition of such extracts 

 must be considerably different from that of extracts of unheated- 

 soils. We decided to investigate first the quantitative differences 

 between the extract of heated-soil and the same kind of soil 

 unheated. The extracts which we analyzed were made by perco- 

 lating the soils in 2 kg. samples with 2 liters of distilled water 

 and taking 50 c.c. of the first liter of extract to come through, 

 as the sample of the extract to be analyzed. The 50 c.c. samples 

 of the extracts were evaporated to dryness in platinum dishes, 

 dried at 108° to constant weight and this weight recorded as 

 total solids. The residues were carefully ashed at a low, red heat, 

 dried and weighed again, this weight recorded as inorganic matter 

 and the difference between this weight and the weight of the 

 total solids recorded as organic matter. We are aware that this 

 method of determination of organic matter by difference of the 

 weight obtained before and after ashing is not strictly accurate, 

 but for the comparative purposes of this work this loss of weight 

 may be used as a satisfactory measure of the organic matter 

 present. 



Determinations were made in this manner upon samples of 

 New York soil, Massachusetts soil, and North Dakota soil. Since 

 it had been noted that the percolation of an extract of heated- 

 soil through an unheated-soil reduced and finally removed its 

 color and again made it an unfavorable medium for Pyronema 

 growth, we repeated this treatment with an extract of heated-soil 

 whose composition was known and determined the change in com- 



