110 HEART-ROT 



present the mycelium was not considered as definitely- 

 belonging to the fungus. This precaution was especially 

 necessary ^^'ith cultures on soils which had not been sterilized, 

 since many sajDrophytic fungi (especially Penicillmm 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, 



Tlie clianges in the substratum, induced by autorlaving, 

 wliicli might account for tliis are : 



1. Destruction of rival organisms. 



2. (,'hemical changes induced by boihng. 



Both these effects are probably of imjjortance, and they 

 must be considered separately. 



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

 sterilized soil other fungi sometimes appeared, but they 

 wei-e 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 onnosus, 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 h). Twelve were a\itoclaved and 

 six were not. They were then treated according to the 

 following table : 



CtiUnres No. Infertid in'th 



276-78. Autoclaved conidia. 



279-81. Not .sterilized conidia. 



282-84. Autoclavcil niyeeliuin. 



28r)-87. Not H tori! i zed myeeliuin. 



288-90. Autoclaved niyceliinn ;Mid a, litlle uuslerilized soil. 



291-9.'?. Autoclaved conidia and .i. little unsterilized soil. 



The results a\ ere : 



276-78. Very good growth. 

 279-81. iWteriaonly. 

 282-84. Very good growth. 

 285-87. Bacteria only. 



988 on {^^^^ growth at first of mycelium of vaiious fungi, but later 

 restrictcfl to mvceiiiini above the soil and bacteria in (ho 



291-9:5. 



.soil i(se 



