HEART-ROT 111 



The effect of the addition of bacteria is clearly shown in 

 fig, 45. It is thus proved that the unsterilized soil contains 

 some factor which is very strongly inhibitive to the gro\vth 

 of the mycelium of Fomes annosus, and this factor appears 

 to be bacterial. 



2. It is evident that chemical changes are induced by 

 boiling hi^mus soils containing roots and other plant remains 

 which have not been completely disorganized. When twigs 

 and wood blocks are autoclaved in test-tubes, a brown stain 

 nearly always runs down on to the cotton-wool at the 

 bottom of the test-tube. When infected with Fomes annosus 

 tlie latter grows down on to the cotton-wool and flourishes 

 on the stained portion. No doubt a similar liquid escapes 

 from roots into the soil containing them when the whole is 

 boiled, and this probably assists the growth of fungus 

 mycelium. (This, however, cannot apply to such arable 

 soils as / and g, which contained no organized remains.) 

 There is also a physical change, for soil which is autoclaved 

 becomes very evenly moistened, whereas soils which have 

 been diy steriUzed and subsequently wetted are very 

 difficult to moisten evenly, and this may partially account 

 for the poor growth of mycelium on dry-sterilized soils. 



From the foregoing experiments it is clear that the 

 mycelium of Fomes annosns will grow on soils under certain 

 conditions. One condition is the absence of a certain 

 bacterium which is so frequently present in the soil as to 

 inhibit the mycelial growth in all my cultures on unsterilized 

 soils. These experiments were all performed in the summer, 

 when bacterial activity is at its greatest. It is possible that 

 in the spring, when bacterial growth is less active, more 

 auspicious conditions tor Fomes mycelium may obtain. 



lufectlon experiments. A series of infections was made 

 on two-year-old potted plants of larch and spruce. 



These were designed to answer the following questions : 



1. Can un wounded roots become infected with the 

 fungus ? 



2. Can infection take place through slight wounds ? 



3. Can infection take place through dead roots V 



