222 ON TREES. 
be forewarned of the coming ruin. The disease 
which causes the destruction takes place in the oak ; 
but more frequently in the sycamore; and most 
commonly of all in the ash. We will select this 
last tree by way of elucidation. 
Often, when arrayed in all the bloom of vegetable 
beauty, the ash tree is seen to send forth from its 
bole, or from some principal branch, a small fungus, 
which, during the summer, increases to a consider- 
able size. It ripens in the autumn, and falls to the 
ground when winter's rains set in. The bark through 
which this fungus sprouted is now completely dead, 
though it still retains its colour; and that part 
of the wood from which it proceeded is entirely 
changed in its nature, the whole of its vitiated 
juices having been expended in forming and nourish- 
ing the fungus. Nothing remains of its once firm and 
vigorous texture. It is become what is commonly 
called touchwood, as soft and frangible as a piece 
of cork, which, when set on fire, will burn like 
tinder. In the mean time, the tree shows no sign of 
sickness ; and its annual increase goes on as usual ; 
_ till, at last, the new swelling wood closes over the 
part from which the fungus had grown, and all 
appears to go on right again. But, ere the slow 
process arrives at this state, the titmouse or the 
woodpecker will have found an entrance, and a place 
of safety for their incubation. They quickly per- 
forate the distempered bark ; and then, the tainted 
wood beneath it yields to their pointed bills, with 
which they soon effect a spacious cavity. 
Here then we have the whole mystery unfolded. 
