Shade Tree and Timber Destroying Fungi. 



231 



of the tree. Tliis is probably due to the structure of the wood. 

 It grows in three different directions : parallel with the axis of 

 the tree trunk, i. c, up and down ; radially, from the center 

 toward the periphery ; and tangen 

 tiallv. At one stage of development 

 the mycelium may be very profuse ajid 

 abundant. It then is present in the form 

 of cords or strands Avhich lie radially or 

 tano-entiallv in the channels which have 

 been dissolved bv the action of the funo-us 

 ferment on the wood. These strands lie 

 quite close together and are parallel. After 

 being developed in considerable abundance 

 the strands of mycelium largely disappear 

 having burrowed open channels and fur- 

 rows through the wood in the radial and 

 tangential directions. 



Shrinkao:e of the wood occurs at the same 

 time because of the disappearance of a con- 

 siderable content of the Avater and of the 

 wood substance. This shrinkino; results in 

 checking the wood into numerous minute 

 cuboidal blocks, marked off primarily by 

 the position, and solvent action of, the my- 

 celium. This becomes more pronounced if 

 the wood dries, if the tree is cut or if l)locks 

 of the wood are cut from the trunk and al- 

 lowed to dry. In the early infection of the 

 wood, and the early stages in the advance of 

 the mycelium, before the larger strands have 



become established, the openings made by ^^•- Red spruce affected with 



. '' Polyporns horealis. 



the mycelium are very mnmte. They take 



the same directions as the larger openings. In fact the mycelium, 

 instead of making a general attack upon the tissues, begins its ad- 

 vance at certain regularly separated points, and then extends along 

 in parallel lines. If the wood is cut out at this early stage, one can 

 see these minute perforations thickly scattered over the exposed sur- 



