12 THE POLYPORACEAE OF WISCONSIN. 



In all cases where living trees are infected it was found that they 

 had been wounded, and in most cases pilei were growing out of the 

 wound or out of the bark in the immediate neighborhood. In one 

 case the fungus had evidently gained an entrance through a wound 

 caused by the breaking of a limb and from here had spread into the 

 trunk. 



This species is found abundantly in all parts of the state, and 'is 

 confined chiefly to the hosts named above. In the northern part of 

 the state where birch is plentiful, it is most abundant on dead birch 

 logs and limbs. I never found it on living birch trees. 



In the southern part of the state it is most abundant on oak and 

 poplar. The poplar is apparently usually attacked when dead, pilei 

 on living trees being quite rare. 



In all cases which I have observed, trees infected with this fungus 

 were found to have been wounded and usually pilei were growing 

 out of the wounds and about them. A typical case was that of the 

 poplar (Populus deltoides) from which specimen No. 226 was taken. 

 The tree was about eight inches in diameter and could not have been 

 more than twenty years old. About two feet from the ground there 

 was a wound about ten inches long and three to four inches wide. The 

 process of healing had progressed for several years. The exact time 

 was not determined. In and about this wound there were numerous 

 pilei of P. pergamenus. The disease had not spread very far, for 

 pilei were found only a few inches above and below this wound. I 

 have found no more exact data regarding the rapidity of spread in 

 either poplar or oak. However, since oak trees are frequently found 

 covered from top to bottom with pilei, one is inclined to think that 

 the disease spreads more rapidly in oak. 



In general, the decay is a sap rot and is somewhat similar to that 

 produced by P. abietinus in the Coniferae. Only the sapwood is af- 

 fected, and this only to a depth of an inch or two. The wood, es- 

 pecially that of the oak, becomes much lighter in color and weight. 

 Oak wood thus decayed is of the color of poplar but the grain of the 

 wood still appears unchanged. The resistance of the wood fiber is 

 completely destroyed, so that it is possible to rub most of it into a 

 white powder between the fingers and thumb. If sections of this wood be 

 treated with phloroglucin and hydrochloric acid, they will show abund- 

 ant lignose still present ; but sections treated with zinc chloriodide show 

 also some traces of the cellulose reaction. 



These changes do not show quite so clearly in poplar. This may 

 be due to the fact that the color of poplar is naturally light and the 

 texture of the wood is soft and spongy. 



