122 HEART-ROT 
I sought for a similar line of resin in other roots, but they 
were too far rotted to show any trace of it. Thus, though 
these roots are killed because they grow deeply, it is not 
necessary that their point of infection is deep. 
The statement that larch is more liable to heart-rot m 
pioneer stands than in subsequent rotations is not accepted 
by all writers on the subject. In particular, Elwes (Elwes 
and Henry, 1907, vol. ii, p. 363) holds that the rot is more 
often found in the second rotation. This runs directly 
counter to my experience, and the issue can only be settled 
by the counting of woods in which the incidence of heart- 
rot has favoured Elwes’s view or mine. In discussing the 
question, Elwes does not say which of the heart-rots he 
was referring to, whereas my observations are only con- 
cerned with Fomes annosus. Ribbentrop (1908) shows that 
in Germany the first rotation has given most trouble with 
root-rots generally. 
Methods of prevention. The only preventive measure 
which, as far as I know, has been recommended for defence 
against Fomes annosus, is digging a trench round all the 
infected trees. This method was adopted by Hartig in the 
forests near Eberswalde, and the trenches were apparently 
dug with the object of cutting off all the roots so that infec- 
tion should not pass from root to root from infected trees 
to other parts of the forest. Kienitz found that, in one of 
the trenches that Hartig had cut, fructifications developed 
on the cut and exposed roots, so that in this case the remedial 
measure proved to be a source of danger. He referred to 
the treatment as ‘ waldverderblich ’, an expression which 
Brefeld quotes with relish. Hartig replied that a trench 
could easily be watched for fructifications which could be 
removed, and persisted in his recommendation. But the 
conidia discovered by Brefeld present a fresh difficulty. 
These cannot be removed, for they cannot generally be seen. 
And now that we know that the mycelium can grow in the 
humus itself, a trench does not seem a likely method of 
preventing its further expansion. 1 have found, however, 
that when 10 per cent. of lime is added to humus soil, the 
