136 



Mycologia 



produced when the Pyronema has been planted in cultures already 

 thoroughly contaminated with other fungi. 



A fresh culture on agar in which the mycelium was radiating 

 equally in all directions was contaminated by placing a drop of 

 water rich in bacteria directly in front of the advancing mycelium. 

 In a short time the water had evaporated, leaving only the con- 

 taminated spot. The mycelium continued to grow on both sides 

 of the spot but refused to cross the infected area. Later, it grad- 

 ually surrounded this area, which was apparently unfavorable to 

 its growth. 



In no case have I failed to produce an abundant crop of fruit 

 in three to six days on soil sterilized under high steam pressure 

 or with dry heat at a high temperature when such soils have been 

 inoculated with the spores of the fungus. Indeed, such condi- 

 tions are so favorable that it is difficult to prevent the fungus from 

 invading such places even when not inoculated. On the other 

 hand, in no case have I been able to produce more than a begin- 

 ning of growth on unsterilized soil. Soils sterilized at low tem- 

 peratures often produce a scant growth of ascocarps, which are, 

 for the most part, devoid of the normal color. 



The observation is made by Dr. R. A. Harper* that this plant 

 also occurs on damp, well-rotted leaves where there has been no 

 fire. I can account for this only on the ground that the leaves 

 have been previously sun dried and subjected to natural condi- 

 tions of sterilization, for in my experiments here every attempt 

 to grow this fungus on unsterilized materials has failed. It is 

 quite probable that other conditions of sterilization might give 

 the same results as those produced by fire, but this point has 

 not yet been demonstrated. 



Methods of Cultivation for Study 



The cultivation of fungi under artificial conditions is compara- 

 tively easy when we are able to meet the conditions in the labo- 

 ratory under which they normally occur in nature. The appar- 

 ent preference of this species for conditions of sterilization render 

 it unusually favorable for cultivation under artificial conditions. 



* Sexual Reproduction in Pyronema confluens and the Morphology of the 

 Ascocarp. Ann. Bot. 14: 321. 1900. 



