THE LARCH CANKER 73 
thereby reduce its vitality and power of resistance to 
canker. Douglas fir grows well with larch up to twenty or 
thirty years, but on suitable soil for Douglas the larch is 
then suppressed. This mixture may be recommended 
where pure Douglas stands are ultimately required, and 
it is probably preferable to Douglas planted pure in the 
first instance, but mature larch can seldom be grown in this 
association. 
The question of site is of less importance. Healthy trees 
can be grown at any reasonable altitude in Britain, and 
woods in low-lying localities may be just as healthy as those 
on hills. Damp hollows, however, where there is danger of 
cold stagnant air collecting, should be avoided, as larch 
is here especially liable to damage by spring frosts. Very 
poor sandy soil is no doubt unsuitable for growing larch, 
and on heavy clay other trees are likely to be more profit- 
able, but between these limits there is a wide range of soils 
in which larch can be satisfactorily grown, when mixed 
with other trees. A fuller account of the sylvicultural 
requirements of the larch will be found in Chapter X. 
SUMMARY OF CHAPTERS ON LARCH CANKER 
Larch canker, which is one of the most virulent diseases 
of forest trees, has been known in this country since the 
carly part of the nineteenth century, and has becn described 
in detail by Berkeley, Willkomm, and Hartig. Subsequent 
writers have not added anything of first importance to our 
knowledge of the disease. 
The canker is due to the mycclium of the fungus Dasy- 
scypha calycina, which can live either as a saprophyte or as 
a parasite on the larch tree. Dead branches are usually 
filled with the mycclium of the fungus, which makes small 
cup-shaped fructifications on the surface of the bark. 
Under suitable conditions the mycelium gains admission 
to the cortex and phloem of living parts of the tree, and 
can .then cause canker. By killing the cambium at any 
spot it prevents further growth in thickness at that point, 
and each year it kills a larger and larger area of cambium, 
