18 THE POLYPORACEAE OF WISCONSIN. 



inches in diameter. On the knobs so formed the small pilei were found, 

 and these were the only places at which the rot communicated with 

 the surface. No other wound was found. In this region the rot had 

 developed most vigorously, all of the heartwood being affected and 

 here and there places in the sapwood also. From here the rot spread 

 upward and downward. The horizontal spread is peculiar. At the 

 place of infection the mycelium spreads horizontally as well as up and 

 down, but not so rapidly. When this mycelium has succeeded in get- 

 ting a good foothold in a ring of growth or a number of rings, it fol- 

 lows the ring around the tree and at the same time grows up and down 

 in the same ring or rings. This gives the rot the ring form which is 

 so common, and shows that the mycelium spreads more easily tangen- 

 tially and longitudinally. Another white pine twenty-five years old 

 was studied. This tree, to all appearances, seemed to be perfectly 

 sound and healthy. However, at the end of a branch stub one foot 

 above the ground a very small pileus was found, measuring about one- 

 half inch in width and a little less in length. At this place there had 

 been a wound which had healed over pretty well. The tree, which was 

 about forty feet high with a diameter at the base of eight inches, was 

 cut down and split through the center. The characteristic greyish 

 brown decay was found, extending from a few inches under the ground 

 to nearly four feet above the ground. 



The decayed area was widest about a foot above the ground, where 

 the pileus and the wound were found, being nearly one inch in di- 

 ameter. The tree had been wounded about eighteen years previously, 

 when it was only seven years old. If infection took place at once the 

 fungus was of very slow growth. However, it may have taken place 

 during any of the succeeding eighteen years, there being nothing to 

 ehow when it did occur. In this case the rot was not distributed m 

 rings, as in the log described above. Only the heartwood in the cen- 

 ter was decayed to a height of nearly four feet. Usually the wood 

 turns to a dull pale brown color, but in this case it was a light grey- 

 brown, lighter than the sound heart wood. The little holes and cavi- 

 ties mentioned by Von Schrenk for tamarack and spruce were just be- 

 ing formed. 



The mycelium is quite vigorous in hemlock, but less so in the pine. 

 On the whole, it seems that the growth and spread of the mycelium is 

 much slower in white pine than in any of the other conifers. So that 

 if the trunk of a tree like the big one described above is almost entirely 

 decayed within, it must have taken the greater part of a century to 

 accomplish the work. 



