138 



Mycologia 



the species, it is probably the most practical medium to be 

 employed. 



If plants are desired for sectioning, soft materials, such as 

 broken leaves, may be placed on the soil and sterilized. In this 

 case the fruit is formed in clusters on the leaves and soil. The 

 pieces of leaves may then be removed, imbedded, and sectioned in 

 the ordinary way, or the plants may be scraped off from the leaves 

 and mounted and studied from the gross material. 



Summary 



1. Pyronema omphalodes, which normally occurs on burnt 

 places, can be successfully cultivated on nutrient media, produc- 

 ing sex organs on the fifth or sixth day and mature ascocarps in 

 about ten days from the time of the planting of the spores. 



2. This fungus will produce an abundance of fruit on soil or 

 leaf-mold which has been sterilized by heating to high tempera- 

 tures (no° C. or over), but refuses to produce fruit or any con- 

 siderable mycelium on unsterilized soil or soil heated to low 

 temperatures (less than 95 ° C). 



3. Sterilization by steam serves the same purpose as steriliza- 

 tion with dry heat, provided the soil is sterilized under sufficient 

 pressure (5 lbs. or over). Soil sterilized under low pressure (2 

 lbs. or less) produces fruit only sparingly. 



4. The time required to produce fruit on soil, as well as the 

 abundance of the fruit itself, varies with the temperature to which 

 the substratum has been subjected. Soil sterilized at 95 0 C. has 

 produced no fruit; soil sterilized at no° C. produces a fair quan- 

 tity of fruit; while soil sterilized at I35°-I45° C. produces fruit 

 in abundance. The length of time of the application of the heat 

 also has some influence. 



5. Sterilization of soil by heat apparently brings about some 

 change in the soil other than the simple elimination of competition 

 in the destruction of bacteria and other fungi, which changes 

 appear to be of vital importance in the cultivation of fungi which 

 normally grow on burnt soil. 



