7 



of the infection (fig. 7). After the branch has been killed the 

 fungus grows more rapidly through its tissues, and soon pro- 

 duces the characteristic fruiting pustules over its surface in the 

 form of dark brown, powdery, and erumpent nodules 1-3 mm. 

 (^-i inch) in diameter (fig. 8). 



The production of sprouts or "suckers" just below a lesion 

 is one of the marked characteristics in either the canker or semi- 

 diffuse forms of the disease (figs. 11 and 12). This production 

 of vigorous sprouts occurs as soon as the trunk has been girdled, 

 and they may be few in i^umber or sufficiently numerous to make 

 a conspicuous clump. 



The final result of the disease is the death of the tree, but in 

 the extreme canker type there is a rather prolonged struggle. 

 No cases have been observed where the advance of the parasite 

 has been permanently checked. It is apparently the diffuse type 

 of the disease that is exacting the larger toll, if we may judge 

 from observations in certain localities where the disease is es- 

 pecially prevalent. The disease is especially serious since there 

 is a marked tendency to the production of body or trunk cankers 

 only. They may occur at any point from the ground up but 

 they appear to be more common in the lower portions of the 

 trunk. As soon as girdling has been completed the parts beyond 

 the canker must succumb, but even before such a fatal termina- 

 tion, the trunk may be so weakened by the inroads of the fungus 

 as to be unable to withstand the force of strong winds. Many 

 fallen oaks which have been broken at a lesion are silent wit- 

 nesses of the destructiveness of this trouble (fig. 12). UnHke 

 the chestnut bark fungus, the organism in question grows equally 

 well in both bark and wood. It is this disintegration of the 

 wood by this parasite and not by secondary decays that causes 

 the pronounced weakening of the trunk in the region of a canker. 

 The extent to which the fungus invades the wood even in the 

 canker type is shown in Fig. 14, the light area being the por- 

 tion infected. In Fig. 13 the only normal wood remaining shows 

 a Hght color also. 



