110 HEART-ROT 
present the mycelium was not considered as definitely 
belonging to the fungus. This precaution was espec.ally 
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 (sdil 6). 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 mycelinm 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 Fair growth at first of mycelium of vatious fungi, but later 
291-93. ie iba to mycelium above the soil and bacteria in the 
“(soil itself. 
