116 



Mycologia 



these failures. There are however two possible explanations : 

 (i) that the unheated-soil contains a toxin which retards the 

 growth of the fimgus even in the presence of abundant food 

 material, which toxin is destroyed by heat, thus rendering our 

 •problem a double one; and (2) that the nature of the food 

 material itself is changed by the action of the unheated-soil. 



Our experiments indicate that these failures to render un- 

 heated-soil favorable for this fungus are due in part to the fact 

 that the nature of the food material is changed when this is 

 introduced into unheated-soil. This is shown by the fact that 

 if a pot of unheated-soil is saturated with a concentrated extract 

 of heated-soil (reddish-brown in color) and -allowed to stand 

 for a few days, it is found that the extract has almost entirely 

 lost its color. This result may be due to chemical combina- 

 tion or to the adsorptive phenomena shown by many finely 

 divided materials such as animal charcoal, which will completely 

 decolorize large volumes of solutions containing dyes, etc. Quan- 

 titative studies of extracts treated in this manner show that the 

 soluble materials have been reduced to approximately the same 

 amount contained in extract of unheated-soil. This taking out 

 of solution of the soluble materials in heated-soil extract when 

 added to unheated-soil, seems to account for our failure to render 

 unheated-soil favorable to Pyronema in this manner, but it is 

 possible that there are other factors concerned. This is further 

 suggested by the following observation : While it has been im- 

 possible to render unheated-soil favorable to Pyronema by the 

 addition of heated-soil extract, heated-soil which is watered with 

 the extract of other heated-soil is much more favorable than the 

 same kind of soil treated with distilled water, as is shown by the 

 fact that both mycelium and fruit of Pyronema) are produced in 

 much greater abundance on the heated-soil watered with the 

 extract (pL 26). 



V. Heated-Soil and Its Extracts as Nutrient Media for 



Fungi 



In a previous paper, attention was called to the fact that while 

 heating of soil destroys fungi present at the time of heating, it 

 prepares the way for the growth of those species which are intro- 



