30 DISEASES OF DECIDUOUS FOREST TREES. 



igniarius. The fungus gains entrance into the trunk of the tree 

 through some wound; in other words, it is a wound parasite of the 

 most distinct type. An examination of thousands of infected trees 

 has shown without exception that there must be some wound before 

 infection will take place. A careful series of observations has further- 

 more shown that the point of entrance is usually indicated some years 

 later by the location of the oldest sporophores. These sporophores 

 are usually situated on old branch stubs or in holes left when the base 

 of the branch rotted away. 



In a large percentage of cases infection takes place through old 

 branch stubs. The spores of the false-tinder fungus germinate on a 

 stub, and the hypha3 grow down through the wood of the stub until 

 they reach the heartwood of the main trunk; from this point they 

 grow both up and down in the heartwood, usually starting near the 

 pith, and advance concentrically outward. The destruction of the 

 wood follows very shortly after the entrance of the mycelium into the 

 trunk, progressing both outward and up and down as long as the tree 

 lives. The time which elapses between the injuring of a tree and 

 infection necessarily varies, depending chiefly upon the presence of 

 spores and climatic conditions. 



The formation of sporophores takes place usually at the point 

 where infection originally occurred. This can readily be proved by 

 an examination of the diseased area within the trunk, especially 

 during the early stages of the disease. The formation of sporophores 

 subsequent to that of the first one is determined by the location of the 

 tree, the climatic conditions, the size and vigor of the tree attacked, 

 and the number of side branches which may permit the growth of the 

 mycelium from the center to the outside, thereby making possible the 

 formation of additional sporophores. The number of sporophores 

 which will form on a tree is largely determined by the latter fact. 

 Thus, in the aspen, in which wounds made by the dying of the lower 

 branches are healed over with difficulty, the number of sporophores is 

 very much larger on an individual tree than is the case with trees 

 which heal over such wounds more rapidly, like the beech and the sugar 

 maple. It is not uncommon to find a diseased poplar tree with any- 

 where from three to twelve sporophores on various parts of an affected 

 trunk (PL I) ; in the beech and birch a smaller number is the rule. 



The growth of the mycelium of the fungus is usually confined to the 

 heartwood of the trees. Hartig states that the fungus may enter 

 trees by means of slight wounds in the sapwood, and describes the 

 manner in which the fungus starts its development in the sapwood, 

 growing from the sapwood into the heart. His observations refer to 

 the oak, however, with which comparatively little work has been 

 done in this country. 



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