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 
L2 i 
