Seaver-Clark : Studies in Pyrophilous Fungi 117 



duced subsequent to heating. This conclusion was drawn from 

 the observation of such forms as Verticillium, Fusarium, and 

 species of various other genera of the imperfect fungi which 

 gain entrance to the soil through the planting of seeds. The 

 growth of such fungi was much more abundant on heated- than 

 on unheated-soil. 



Our later experiments with heated-soil extracts confirm the 

 above observation. In addition to Pyronema noted above, these 

 extracts are immediately attacked by Penicillium, Mitcor, Asper- 

 gillus, and a number of undetermined, imperfect fungi, which 

 grow in abundance, entirely covering and filling the extracts, espe- 

 cially the stronger ones, while the extracts of the same soils 

 unheated show no fungous growth whatever. The only way in 

 which we have been able to preserve extracts of heated-soils in 

 our laboratory is by sterilizing and tightly sealing them in bottles. 

 In this way we have been able to preserve them in excellent condi- 

 tion, while if not sterilized and tightly sealed they are soon dis- 

 integrated through the action of bacteria and fungi {pi. 2^, f. 2). 



In our studies of the Iowa Discomycetes it has been observed 

 that about five per cent, of the species of this group reported 

 from Iowa occur only on burned places. That such habitats are 

 unusually favorable to the growth of saprophytic fungi is beyond 

 question. 



It is likely that many of the beneficial results obtained through 

 the sterilization of soils, which effects have been attributed to the 

 destruction of harmful fungi and bacteria in the soil, are due 

 more to the chemical changes accompanying sterilization than to 

 the sterilization itself. 



VI. Distillates from Heated-Soil Extracts 

 Some heated-soil extract of a brownish color was distilled to 

 one half of its original volume and the distillate collected. The 

 residual solution in the flask had the rather pleasant odor of the 

 heated-soil extract but the distillate had the pungent odor which 

 is also present in the original extract. Both the distillate and the 

 liquid in the distilling flask were acid to litmus. We thought that 

 possibly we had been able to separate the toxic from the non-toxic 

 acid substances by their difference in volatility and for this reason 



