12 A DISEASE OF THE WHITE ASH. 



change more slowl}'. This g'ives rise to a banded appearance near the 

 edge of the diseased area, more pronounced in some places than in 

 others (see the lower part of PI. I, fig. 2). Ultimately the whole wood 

 ring turns into a looseh'^ connected mass of fibers. 



When the tree is first attacked it appears as if the changes described 

 take place simultaneoush" over a large area (3 square inches in the 

 tree shown in PI. I, fig. 2), and that thereafter the change from sound 

 to decaj'ed wood goes on more slowly. This is the case in diseases of 

 other trees, and is possibly accounted for by the fact that at first no 

 products of metabolism interfere with the growth of the fungus, while 

 later on these may retard gTowth to some extent. 



The completely rotted wood is straw colored, verj^ soft and nonre- 

 sistent, and readilv absorbs water. The disintegTating chano-es are 

 by no means uniform, as a glance at PI. I will show. The diseased 

 areas have very irregular shapes; sometimes they involve the whole 

 trunk, at other times only one side, depending somewhat on the point 

 of infection and the shape of the trunk. In the trunk shown in the 

 lower figure on PI. I the fungus was growing in the seventh ring 

 from the bark. 



THE SPOROPHORE. 



The sporophores of Polyporusfraxinojyhihis appear around the base 

 of branch stubs, or in wounds, very soon after the original infection 

 (PL II). With some trees — for instance, Pinus ecliinata attacked by 

 Trametes pini — it appears that a good deal of wood is destroyed before 

 2i\\\ fruiting bodies of the fungus form. With the ash, fruiting bodies 

 make their appearance when the wood shows signs of having decayed 

 only a ver}" short distance from the point of infection. In one tree, 

 where the sporophore was developing at a branch stub, the heartwood 

 was actually rotted for a distance of only I inches on either side of the 

 base of the branch, while the characteristic discoloration extended for 

 a foot in both directions from the stub. When the dead branch is a 

 large one, small white knobs grow out at several points near its base 

 (PI. II, fig. 2), often as many as ten or a dozen. These knobs are 

 almost white, \qvj smooth, and adapt themseh^es to the irregularities 

 of the rough bark. When the branch extends out horizontally, the 

 sporophore frequently appears to be hanging from the under side of 

 the branch (PI. II, fig. 1). As the sporophores grow older they extend 

 downward on the bark; in other words, become decurrent behind. 



The mature sporophore is nearly triangular in ci'oss section. 

 Although fairh' regular in form, there are many sporophores which 

 are compound, i. e., composed of several superincumbent shelves or 

 several shelves joined laterally. It has a broad rounded edge, which at 

 first is white and gradualh* tarns darker until it becomes somewhat 

 straw colored. The older portions of the upper surface are dark brown 

 or black, and are very hard and woody. 



