110 HEAET-ROT 



present the mycelium was not considered as definitely 

 belonging to the fungus. This precaution was especially 

 necessary with cultures on soils which had not been sterilized, 

 since many saprophytic fungi (especially Penicillium spp.) 

 as well as bacteria made their appearance. The most 

 striking feature of this table is the failure of the fungus to 

 grow on any unsterilized soil and its growth on all soils 

 when autoclaved. 



The changes in the substratum, induced by autoclaving, 

 which might account for this are : 



1. Destruction of rival organisms. 



2. Chemical changes induced by boiling. 



Both these effects are probably of importance, and they 

 must be considered separately. 



1. Destruction of rival organisms. In cultures on un- 

 sterilized soil other fungi sometimes appeared, but they 

 were not constant. A certain species of bacterium, however, 

 nearly always grew abundantly and formed a white covering 

 over part of the soil. It seemed possible that this bacterium 

 was destructive to the mycelium of Fomes annosus, and to 

 prove this a series of cultures was made in the following 

 way. Eighteen test-tubes were filled in the usual way with 

 sand and oak humus (soil b). Twelve were autoclaved and 

 six were not. They were then treated according to the 

 following table : 



Cultures No. Infected with 



276-78. Autoclaved conidia. 



279-81. Not sterilized conidia. 



282-84. Autoclaved mycelium. 



285-87. Not sterilized mycelium. 



288-90. Autoclaved mycelium and a little unsterilized soil. 



291-93. Autoclaved conidia and a little unsterilized soil. 



The results were : 



276-78. Very good growth. 

 279-81. Bacteria only. 

 282-84. Very good growth. 

 285-87. Bacteria only. 



288-90 (^ a " % g row th at first of mycelium of vaiious fungi, but later 

 ' restricted to mycelium above the soil and bacteria in the 

 soil itself. 



