TREE ROOT ROT 203 



portions attacked are vital parts, the young wood, cambium, 

 and bark, and as the trunk is attacked simultaneously all 

 round, the tree soon succumbs to its enemy. The mycelium 

 of A, mellea is so thoroughly characteristic that it can be 

 recognised with certainty, even when the fructification is 

 absent. On examining roots attacked by this fungus, its 

 mycelium is seen under the form of blackish, cordlike 

 strands of the thickness of fine twine, which creep over the 

 surface of the roots and the base of the trunk close to the 

 ground, and in addition radiate in the ground on every 

 side, where they continue to grow and increase in length 

 until they come in contact with the roots of neighbouring 

 trees, which are attacked, and become in turn centres from 

 which the mycelium spreads in the ground as before, in 

 search of new victims. 



The black, cordlike strands of mycelium, known as 

 rhizoinorphs^ do not penetrate the roots, but give off 

 irregularly arranged delicate branches at intervals ; these 

 branchlets enter the roots and form thin white sheets of 

 mycelium running between the bark and the wood, and are 

 known as subcortical rhizomorphs. Hyphae from these 

 latter penetrate the wood for a short distance, mostly 

 following the medullary rays, branches of hyphae passing 

 into the vessels of the wood, which soon become choked 

 with a dense mass of mycelium. In conifers the mycelium 

 fills the resin canals, and destroys the cells forming their 

 walls, the resin exuding through the bark in large masses 

 at the base of the trunk. 



Preventive Means. — In orchards, etc., where only few 

 trees are attacked, it is advisable, as suggested by Hartig, 

 to isolate such trees, by digging a narrow trench about a 

 foot deep round each, at some distance from the trunk ; 



