SHADE TREE AND TIMBER DESTROYING FUNGI. 205 



top of the tree. Its presence on the roots was determined by 

 the occurrence of the fruit bodies from 

 a few places on exposed parts of the 

 large roots, while external evidence of 

 its having reached the top of the tree 

 was shown by a number of dead limbs 

 in the top, some of which had fallen. 

 Evidence of its having reached the top 

 was also found on cutting down the tree, 

 and taking out sections at different points 

 in the trunk. Here was found an abund- 

 ance of mycelium and the heart wood 

 was in an advanced stage of decay. 



The mycelium advances in certain 

 definite directions in the wood of the 

 tree. This is probably due to the struc- 

 ture of the wood. It grows in three 

 different directions : parallel with the 

 axis of the tree trunk, i. <?. up and down ; 

 radially, from the center toward the 

 periphery ; and tangentially. At one 

 stage of development the mycelium may 

 be very profuse and abundant. It then 

 is present in the form of cords or strands 

 which lie radially or tangentially in the 

 channels which have been dissolved by 

 the action of the fungus ferment on the 

 wood. These strands lie quite close 

 together and are parallel. After being 

 developed in considerable abundance 

 the strands of mycelium largely dis- 

 appear having burrowed open channels 6i.Red spruce affected 

 and furrows through the wood in the with Polyporus borealis. 

 radial and tangential directions. 



Shrinkage of the wood occurs at the same time because of the 

 disappearance of a considerable content of the water and of the 

 wood substance. This shrinking results in checking the wood 

 into numerous minute cuboidal blocks, marked off primarily by 



