2 INTRODUCTION 
long time without any considerable repairs, whilst the other 
decayed very rapidly, and from this comparison the superio- 
rity of Scotch larch over Scots pine, for durability, was 
considered to be pretty well established. If Scotland could 
grow larch timber which was more durable than Baltic fir, 
there was no reason to despair of British forestry, and the 
reputation of larch, already great, was still further enhanced. 
So foresters continued to plant larch wherever the site 
was suitable, and in a great many places where it was not. 
It was used for railway sleepers and other outdoor purposes, 
and further experience confirmed the belief in its capacity 
for bearing exposure ; and it must have been at this time, 
about 1840 to 1850, that its popularity reached. the height 
from which it subsequently and continuously declined. It 
was fast-growing, straight, and easy to handle, but it had 
one great weakness: it became extremely liable to disease. 
A book on the larch, written by Mackintosh in 1860, is 
a sufficient index of the change that had come over the 
opinion of foresters, and nearly all writings since this date 
have partaken of the nature of apologetics for a tree that 
had failed to fulfil its early promise. 
The disease that Mackintosh was most concerned with 
was variously known as heart-rot, dry-rot, piping, pumping, 
and internal decay, and was believed to be caused by a 
fungus which they called Polyporus destructor. Exactly what 
disease this was is not clear, but it was no doubt one of the 
heart-rots as we know them to-day, and very likely Fomes 
annosus was alone responsible for it. In addition to this, 
larch canker was becoming frequent, and in time proved to 
be an even more serious trouble than heart-rot, or, at any 
rate, one that was more visible to the eye and consequently 
more feared. At the present day there is scarcely a young 
plantation anywhere in the country which is entirely free 
from canker, and felling all too frequently discloses the 
presence of heart-rot as well. So larch is no longer the 
- favourite tree that it was, and the tendency is to use it less 
often in pure plantations, though it is still very frequently 
employed in admixture with other trees since canker is 
