14 



these holes and grows in the sapwood of the tree, destroying it in a few 

 months. Whether it grows there while the tree is still alive, and what 

 its possible relations ma}^ be to the Dendroctonus, are problems yet to 

 be solved. In many parts of the Maine woods every tree where the 

 beetles had been or were still active was covered with the rounded 

 fruiting organs of this Polyporus. (See PI. I, fig. 2.) Their association 

 with this Polyporus offers a promising field for study. The holes made 

 b}^ the beetles allow the spores of several other fungi to enter, notably 

 those of Polypomis ])inicola. These germinate and grow throughout 

 the heartwood, rendering it worthless in a very short period. 



The possible role which beetles and boring larvae ma}^ play in carry- 

 ing the spores of a fungus from one tree to another will be referred to 

 below. These few instances will serve to show that it is all important 

 that a study of the insect and fungus enemies of a tree should be made 

 hand in hand. 



There are grave iiiherent difficulties in determining the exact cause 

 of death of a large tree, for there are many factors which may influence 

 its growth so that the tree becomes weakened. There is a widespread 

 opinion that insects or fungi will not attack an absolutely healthy tree, 

 but that the latter must be more or less weakened before such an 

 attack takes place. That this is not always the case need hardl}" be 

 said, but the mere fact that a fungus is growing in the tree or an insect 

 is at hand upon it is no positive proof that one or the other is the 

 active agent in bringing about its death. Such evidence, particularly 

 if oft repeated, will become ver}^ valuable when taken in conjunction 

 with other proofs. 



SCOPE OF THIS REPORT. 



In the following a number of fungi will be described, together with 

 the characteristic changes which their mycelia induce in the wood of 

 the trees in which they grow. These fungi were found again and 

 again, always associated wdth the forms of decay ascribed to them, and 

 never was such decay found without the fungus in question, or with- 

 out a mycelium from which the fruiting portion of the fungus devel- 

 oped. These fungi occurred on all coniferous forest trees, with few 

 exceptions. Some of them started in the living trees and caused the 

 heartwood to deca3^ They were found in large numbers destroying 

 trees injured by insects, and on some tracts where fire had swept 

 through the woods and had injured the bases of the tree trunks sev- 

 eral of them had gained a foothold and had destroyed ever}^ tree thus 

 injured. The principal ones met with were: Polyjyorus sclnoeinitzii 

 Fr. ; P<)lyj)(/rwi 2n'fy(^cola (Swartz) Fr., Tvametes inni (Brot.) Fr. forma 

 ahietis Karsten; Pohjporui^ sitlfure^is (Bull.) Fr. ; and Pnlyponos suh- 

 aci.dus Peck. A number of doubtful forms will be mentioned near the 

 end of this report. 



