214 Practical Forestry 



larch canker owes its origin to the minute spores formed 

 in the fructification of the now well-known fungus Peziza 

 Willkommii. It has been pretty conclusively proved that 

 these spores can only find a footing where the rind of the 

 bark has become in some way injured, such as might be 

 occasioned by the puncture of an insect, by wind, frost or 

 from many other causes. The spores send down their germ 

 tubes into the cambium, between the bark and the wood, 

 where the moisture and nourishment afforded causes rapid 

 development of the fungus. This soon spreads to the cells 

 of the wood, arid the annual layers either entirely cease to 

 grow, or become disorganized and crippled in growth, caus- 

 ing a hollow appearance of the stem at the point of attack. 

 The surrounding bark, by its attempts to heal over the 

 wound, causes a thickened or burly appearance of the trunk, 

 thus imparting to affected trees the cankered, swollen and 

 distorted look that is so distinguished a characteristic. 



The disease appears in this country on the larch, both 

 common and Tyrolese, at all stages of growth up to thirty 

 years, but rarely after that age. I have examined a planta- 

 tion of only four years' growth sadly infested by the Peziza 

 whereas, in other cases, the trees may be fully twenty 

 years old before being attacked. 



Cause. Under what conditions of growth the larch is 

 most susceptible to the Peziza is still a matter of vague 

 uncertainty, but there can be little doubt that an enfeebled 

 constitution, as fully explained in the article on the larch 

 (" Trees for Economic Planting "), aided by our peculiarly 

 erratic climate, has much to answer for. The variableness 

 of our spring weather is, no doubt, one of the predisposing 

 causes of disease, for, although no degree of frost experienced 

 in this country can injure the tree when leafless, yet few 

 are more sensitive when in young foliage. 



Bearing on the subject of the larch disease, I have 

 communications from almost every part of the country, and 

 have personally visited and examined many of the worst 

 infested plantations, particularly in England and Wales. 

 Soil, if we exclude peaty, would seem to have little or 

 nothing to do with encouraging the disease, as I have found 



