Seaver-Clark : Studies in Pyrophilous Fungi 111 



carbohydrates and proteins, the following more or less complex 

 substances; alkaloids, glycosides, tannins, hydrocarbons, resins, 

 etc., it is not difficult to imagine how compounds toxic to the plant 

 might well arise either directly or through bacterial action, slow 

 oxidation or other deep-seated changes. Schreiner has shown 

 that the growth of a plant in a solution makes that solution 

 rather toxic to the growth of the same plant in the same medium 

 because of the throwing off of toxic organic substances, rather 

 than the depletion of the food supply by the growth of the plant. 



All of this shows that in questions of soil fertility for certain 

 plants, we must not only consider what necessary food materials 

 are present but also determine, if possible, whether there are any 

 toxic substances present which would check plant growth even 

 in the presence of an abundant supply of organic and inorganic 

 food materials. 



In order to test the toxin theory with reference to the growth 

 of Pyronema, an extract of unheated-soil was prepared by add- 

 ing four liters of distilled water to two kilograms of unheated- 

 soil. This mixture was stirred frequently and allowed to stand 

 for some time and later filtered and used for the treatment of 

 heated-soil. 



On November ii, 1909, a series of experiments was conducted 

 in which three pots of soil heated to about 160° C. for about two 

 hours (S^, S^, and S^) were used, with a pot of similar soil 

 unheated as a control (C). Pot (S^) and control (C) were 

 treated with distilled water. Pot (S^) was treated with extract 

 of unheated-soil prepared in the above manner, the mixture hav- 

 ing been allowed to stand with frequent stirring for two hours. 

 Pot (S^) was also treated with extract of unheated-soil on the fol- 

 lowing day, the mixture having been allowed to stand for twenty- 

 four hours instead of two as in the preceding experiment. Each 

 was inoculated with Pyronema. 



On November 23, (S^) and (S^) showed fair growth of Pyro- 

 nema especially on the pots, but at this time no fruit had appeared, 

 while (S^) showed good growth of mycelium and fruit. Control 

 (C) gave negative results as usual. 



Other experiments similar to the above were later conducted. 

 In each case the heated-soil treated with the extract of 



