FOMES APPLANATUS 145 



parasite and lives on the wood of the trunks, thick branches, and 

 stumps of forest trees ; and it also produces many thousands of 

 millions of spores each day for about six months of each year. 

 Let us imagine that this fungus has established itself in a tree- 

 trunk in a virgin forest, such as we find in western Ontario, and 

 let us suppose that it has developed a large fruit-body on the tree's 

 exterior. The fruit-body will pour out daily from its hymenial 

 tubes some thousands of millions of spores. What new trees can 

 be infected by these spores ? Certainly not each and even^ one. 

 The bark of a tree, composed, as it largely is, of sheets of cork, 

 and containing, as it does, various special chemical bodies such 

 as tannin, resin, etc., protects the tree's inner tissues from the 

 invasions of parasitic fungi and, in particular, so far as our present 

 enquiry is concerned, from the attacks of wood-destroying fungi. 

 We are therefore safe in assuming that our Fomes cannot gain 

 a new foothold on any tree which has uninjured bark. 



From the foregoing we are forced to the conclusion that the 

 invasions of our Fomes must be limited to trees with wounds, 

 i.e. trees which have had their bark injured and their wood exposed 

 in open wounds through the breaking of branches by the wind, 

 through frost-cracks, strokes of lightning, the fall of dead branches 

 projecting from the tree- trunk, the fall of neighbouring trees, etc. 

 Now in all probability, it is only the larger wounds of a tree that 

 can be used as entrance places by our Fomes. I suspect that no 

 large wood-destroying fungus can enter a tree through very small 

 wounds, such as are made when dead twigs fall from the higher 

 branches and when thin but still living branches are broken from 

 a tree by accident. In most trees, as one may readily realise by 

 observing their growth in successive years, most of the twigs are 

 doomed to die before they become many years old ; and, if one 

 examines the forest floor under Oaks, Beeches, Elms, etc., one finds 

 that it becomes littered every year not merely with the dead leaves 

 but with a great number of dead twigs which have died a perfectly 

 natural death and have been shed by the higher branches. Now 

 if a wound-parasite, like our Fomes applanatus, could obtain entry 

 into the thicker branches and the trunks of trees through small 

 wounds made by the fall of dead twigs and the breaking away of 



