THE HONEY FUNGUS 147 



hyphae woven together into a dense mycelium. But in 

 function they are entirely different from roots, for they are 

 incapable of obtaining moisture or nutriment from the soil 

 in which they are growing. If they are traced back to their 

 base they will be found to originate in a stump, and though 

 they may grow to a considerable length, all their food 

 supplies are drawn from the stump. One of their uses is 

 obvious, viz. to bear fructifications at a distance from the 

 stump ; but they have a still more important function, for 

 when they come into contact with the root of a living tree 

 under favourable circumstances, they penetrate it and infect 

 the new host with the disease. 



It is these rhizomorphs which make Armillaria so difficult 

 to eradicate, for they spread far and wide in the soil, and 

 all the trees in the neighbourhood of an infected stump are 

 liable to attack. 



In addition to the fructifications and the rhizomorphs, 

 there is the mycelium in the tree itself. In the wood the 

 mycelium is too fine to be seen by the naked eye, except 

 for the black line (fig. 65), which can be found in any 

 sections across the base of a trunk during the more advanced 

 stages of attack. In conifers this line is always fine, but in 

 broad-leafed trees it sometimes becomes fairly broad, and 

 is very marked in stumps which are thoroughly rotted. 

 Between the scales of the bark and in the cambium dense 

 layers of white mycelium are formed -which are the surest 

 means of diagnosis in the earlier stages of the disease. 

 They are much thicker than the layers formed by Fomes 

 annosus, and are usually veined. This felted mycelium 

 grows up through the cambium to a considerable height, 

 but when the tree is dead and the bark has become loosened, 

 it is replaced by a tangled mass of flattened rhizomorphs 

 (figs. 63 and 64). These were at one time regarded as a 

 separate species of fungus under the name of Rhizomorpha 

 subcorticalis , distinguished from the rhizomorph in the soil, 

 which was called Rh. subterranea. 



Though the fungus attacks all kinds of conifers, it favours 

 some more than others. Scots pine is probably the most 



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