150 



the attack so vigorous that young trees often succumb in one or 

 two years, and older ones soon lose branches of such size that 

 the vigor of the entire tree is materially impaired and its beauty 

 and usefulness practically destroyed. It is not the primary effect 

 of the fungus on the living tissues of the tree, widespread as this 

 effect often is, that causes the greatest damage ; but the secondary 

 effect of this injury on the remaining portions of the trunk or 

 branch affected ; for it is the habit of the entering mycelium to 

 proceed in a circle about the affected portion until it is completely 

 girdled. This girdling habit 



up and doi 



ithe 



t the infec 



dthe; 



wth of 



ard the current of water and food supply, which 

 is more and more deflected by the invading fungus until finally 

 cut off altogether. 



This is well shown in Fig. 19, which represents a portion of a 

 young tree being girdled by the fungus, viewed from three 

 different, directions. The fungus entered in 1905 through an 

 undressed pruning wound, and grew nearly half-way around the 

 trunk during last season. The first week in May, 1906, when 

 the weather was warm and moist and the inner bark full of food, 

 the mycelium began to grow again, and by May 1 1 it had cov- 

 ered that part of the trunk indicated by the light area in the figure. 

 On May 1 5 the two growing borders had united and the girdling 

 was apparently complete ; though death did not ensue for several 

 days, on account of tissues lying next to the sapwood that still 

 remained uninjured. At this time the leaves of the opening buds 

 were scarcely an inch in length ; too young to have made use of 

 much of the nutriment stored in the stem. 



When the tips of branches are affected, the progress of the 

 disease is of necessity slow, since the affected area is small and 

 the food supply scanty. On the other hand, the base of the 

 young tree is a point of special danger, since the abundance of 

 moisture and food it supplies facilitates the speedy growth of the 

 fungus and thus endangers the life of the entire tree. 



The way in which the fungus in question first enters a chestnut 

 tree is at present largely a matter of conjecture. Twigs, sprouts, 

 nursery trees, branches of various sizes, and trunks a foot or 



