Seaver: Studies in Pyrophilous Fungi 133 



finally mature their fruit and disappear. The species was said to 

 occur on soil sterilized in this manner almost without exception 

 and had been noted for several years past by those carrying on 

 experimental work here requiring the sterilization of soils ; but 

 as the fungus usually appeared before seeds had germinated and 

 apparently did no harm, it did little more than to arouse a passing 

 interest. The attention of the writer was at length called to this 

 fungus and it was identified as Pyronema omphalodes (Bull.) 

 Fuckel. The occurrence of a fungus commonly associated with 

 burnt places on soil sterilized with steam was a fact of unusual 

 interest, since it indicated that charcoal and carbonaceous mate- 

 rials are not necessary to the life of this fungus as was previously 

 supposed. 



In trying to explain these facts it at once became apparent that 

 the high temperatures to which the substrata had been subjected 

 had something to do with the appearance of these plants under 

 the above conditions, but whether the high temperatures had 

 some relation to the spores of the fungus itself in stimulating 

 them to germination or to the substrata only in preparing it for 

 the growth of the fungus was at that time a question. 



During the summer of 1907 the species was again observed in 

 North Dakota, where it occurred on bare soil by roadsides where 

 there was no trace of charcoal, but in places which it is easy to 

 suspect had been fire-swept or subjected to considerable tempera- 

 tures by the heat of the sun and natural conditions of sterilization. 



The last appearance of these plants and the one which has 

 prompted the study of the problem which has been made the basis 

 of the present paper was in agar which had been inoculated with 

 the spores of other fungi in the laboratories of the New York 

 Botanical Garden. The appearance of this fungus, uninvited, in 

 three different cultures at the same time in a laboratory where 

 to my knowledge none of the plants of the genus had been studied, 

 even from dried material, for more than two years was sufficiently 

 mysterious to arouse interest. 



There were two possible explanations of the appearance of this 

 fungus at this time ; one that the cultures had become inoculated 

 with the spores from the air and the other that the spores were 

 present in the cultures and had withstood the process of steriliza- 



