Tree Root-Rot. 



167 



white cobweb-like mycelium, which soon produces blackish, 

 cord-like, radiating strands of mycelium called rhizomorphs. 

 These bodies, which vary in thickness from that of thick 

 thread to moderately thick twine, continue to increase in 

 length, travelling a few inches underground, until they come 

 in contact with the root of a tree, when the cortex is pierced 

 and a firm white sheet of mycelium is formed between the 

 cortex and the wood. This felt gradually passes up the 

 trunk for some distance between the bark and the wood, 

 and also extends into other sound roots. At the same time 

 the rhizomorphs continue to spread over the surface of the 

 roots and the collar, entering the cortex at various points. 

 Delicate strands of mycelium extend from the felt formed 

 under the cortex into tne wood, principally along the medul- 

 lary rays, and thence pass intc the vessels, which soon become 

 choked with a dense mass of mycelium. 



In conifers the mycelium fills the resin-canals and destroys 

 the cells forming their w T alls, the resin exuding through the 

 bark in large quantities and collecting round the collar ; 

 hence the name " resin-flux " sometimes given to this disease. 



At a later stage of the disease the surface of the roots 

 and collar are covered with a white felt of mycelium, which 

 exhibits a pale phosphorescent light in the dark. 



After the death of the tree, numerous stout, branching, 

 black rhizomorphs form a network between the wood and the 

 bark. 



Finally, after a tree has been attacked and the mycelium of 

 the fungus well developed, numerous rhizomorphs spread 

 underground, where they continue to extend until they come 

 in contact with the roots of some neighbouring tree, which is 

 attacked and killed, forming in turn the starting point from 

 which rhizomorphs again wander in search of other victims. 



Preventive Measures. 



There are two methods by which a tree may become 

 infected: — (1) spores; (2) underground rhizomorphs. Infec- 

 tion by means of spores may be prevented by destroying all 

 fungi growing in the neighbourhood of valuable trees. The 

 fungi should be collected and burned ; kicking ever and 



