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 jDreferable to Douglas planted pure in the 

 first instance, but matm-e 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 locahties 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 gromng 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 

 early part of the nineteenth century, and has been described 

 in detail by Berkeley, Willkomm, and Hartig. Subsequent 

 Avi'iters have not added anything of first importance to our 

 knowledge of the disease. 



The canker is due to the mycelium of the fungus Dasy- 

 scypha calycina, which can live either as a saprophyte or as 

 a parasite on the larch tree. Dead branches arc usually 

 filled with the mycelium 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 jihloem 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 Idlls a larger and larger area of cambium, 



