SUSCEPTIHILITY DESCRIPTION. 1 1 



SUSCEPTIBILITY TO THIS DISEASE. 



The (juestion of the relative susceptibility^ of iiidividiml phints to a 

 disease is a most interesting- and at the same time a most obscure and 

 ditticult one to discuss. In the present instance it would seem that 

 there mioht be some relation between the greater susceptibility on the 

 part of the ash near its western limit and its o-enerally weaker devel- 

 opment at this limit. It will be an inteiesting i)oint to detei-mine, for 

 instance, whether the rate with which l)ranch wounds or stul)s heal in 

 Ohio and Pennsylvania is greater than in Missouri and Kansas. That 

 the rate of growth is slower in the Western States we know. 



Pol ifpot-m fraxlnopli lilts has been reported as growing on livino- 

 trees of Fraxinus virldis in Rooks Count.v, Kans." 



METHOD OF ATTACK. 



Pohjporm fraKinop)h'dH!i attacks ash trees of all ages, usually, how- 

 ever, those more than 7 inches in diametei-. The fungus begins its 

 growth in a wound, or more often in a dead branch. It would perhaps 

 be more correct to say that the fungus gains entrance into the tree at the 

 point where the callus touches the branch stub. The branches of the 

 ash are usually inclined upward at a considerable angle, and the callus 

 leaves a groove between its outer surface and the branch stub in which 

 water can collect. From sections of old branch stubs it appears that 

 the earliest signs of fungus action are found in the outer parts of the 

 dead stui) close to this groove. The fungus grows down toward the 

 center of the tree in the outer layers, and from these spreads to the 

 main trunk up and down and lateially. It is quite usual to tind a tree 

 infected at two or more separate points. In a region ^\here the sporo- 

 phores are common and where each tree has many dead branches this 

 is not at all surprising. 



DESCRIPTION OF DISEASED WOOD. 



The wood of the ash is uniformly straw yellow in color and shows 

 little difference in tint between heart and sapwood. A gradual dark- 

 ening of the wood near the center of the tree is the first indication of 

 the presence of the fungus mycelium (PI. I). In an irregular patch 

 the wood looks as if stained, at first a very light brown, later on a 

 darker brown. The broad bands of summer wood show this change in 

 color most conspicuously. The next stage in the disease is marked b}^ 

 a bleaching of the color in the spring duct layers; these gradually turn 

 back to the original straw color and then turn white in spots. The 

 white color becomes more marked until the entire spring wood is 

 white. It has a disintegrated appearance by this time, and shortly 

 afterwards all the fibers fall apart. The dense bands of summer wood 



« Ellis & Everhart. X. A. Fungi, No. 3302. 



